OCR A 2.1.1 Atomic Structure and Isotopes REVISION

Summary

In this educational video, Chris Harris from Allert Tutors explores atomic structure and isotopes as per the OCR specification. Harris explains the atom's components, including protons, neutrons, and electrons, and their charges and relative masses. He delves into ions, isotopes, and their differences, using oxygen as an example. The video also covers the historical development of atomic models, from Dalton's spherical atoms to Rutherford's nuclear model and Bohr's energy shells. Harris teaches how to calculate relative atomic mass using mass spectra, a method for measuring isotope masses, and identifies elements like chlorine and germanium through this process. The video is a valuable resource for students revising for exams, with supplementary PowerPoints available for purchase.

Takeaways

• 🔬 The video provides a revision overview of atomic structure and isotopes for the OCR specification.
• 🌐 The presenter, Chris Harris from allertutors.com, offers PowerPoints for purchase to aid in revision and note-taking.
• 💡 Atoms consist of a nucleus with protons and neutrons, and electrons orbiting in shells, with the nucleus being very small relative to the atom's size.
• ⚛️ Protons have a relative charge of +1 and mass of 1, neutrons have no charge and a relative mass of 1, and electrons have a charge of -1 and a very small relative mass.
• 📊 The periodic table lists elements with a mass number (larger number) indicating the sum of protons and neutrons, and an atomic or proton number (smaller number) indicating the number of protons.
• 🔋 The number of protons in an atom equals the number of electrons, and the number of neutrons can be calculated by subtracting the atomic number from the mass number.
• ⚡ Ions are atoms that have lost or gained electrons, resulting in a different number of electrons and protons, unlike neutral atoms.
• 🌐 Isotopes are variants of an element with the same number of protons but different numbers of neutrons, leading to different masses.
• 📈 The history of atomic models includes significant contributions from John Dalton, J.J. Thomson, Ernest Rutherford, and Niels Bohr, each refining the understanding of atomic structure.
• 🧬 Mass spectrometry is a technique used to measure the mass of isotopes in an element, and the relative atomic mass of an element can be calculated from the mass spectrum data.

Q & A

What is the main topic of the video presented by Chris Harris?

The main topic of the video is the atomic structure and isotopes, specifically tailored for the OCR specification.

How can viewers obtain the PowerPoints used in the video?

Viewers can purchase the PowerPoints by clicking on the link provided in the description box below the video.

What are the three main components of an atom as described in the video?

The three main components of an atom are protons, neutrons, and electrons.

What is the relative charge and mass of a proton as mentioned in the video?

A proton has a relative charge of plus one and a relative mass of one.

How does the video explain the difference between the number of protons and neutrons in determining the mass number of an element?

The mass number of an element is determined by the sum of the number of protons and neutrons in the nucleus.

What is an ion according to the video?

An ion is an atom that has lost or gained electrons, resulting in a different number of electrons and protons.

What is the key difference between isotopes as explained in the video?

Isotopes are variants of an element with the same number of protons but different numbers of neutrons.

How does the video describe the historical development of the atomic model from John Dalton to Neils Bohr?

The video outlines the progression from Dalton's solid sphere model, to Thomson's plum pudding model, Rutherford's discovery of the nucleus, and finally to Bohr's model with fixed energy shells.

What is the significance of the gold leaf experiment in the context of the video?

The gold leaf experiment, conducted by Rutherford, provided evidence for the existence of a small, positively charged nucleus within the atom by observing the deflection of alpha particles.

How can the relative atomic mass of an element be calculated from its isotopes, as per the video?

The relative atomic mass can be calculated by multiplying the mass of each isotope by its percentage abundance and summing these products, then dividing by the total percentage abundance.

What is the purpose of Mass Spectra as explained in the video?

Mass Spectra is used to measure the mass of isotopes in an element by determining the mass-to-charge ratio of the ions produced when electrons are removed from the atoms.

Outlines

00:00

🔬 Atomic Structure and Isotopes Overview

This paragraph introduces the video's focus on the OCR atomic structure and isotopes, presented by Chris Harris from Allert Tutors. The video aims to provide a revision overview based on the OCR specification. Chris mentions that the PowerPoint slides used in the video are available for purchase, which can be beneficial for revision on various devices. The content is structured around the specification points, starting with an explanation of the atom's structure, including protons, neutrons, and electrons, and their relative charges and masses. The paragraph emphasizes the importance of understanding the atomic structure, specifically the relationship between protons, neutrons, and electrons in an atom, and how to calculate the number of neutrons. It also touches on the concepts of ions and isotopes, explaining the difference between atoms and ions, and how isotopes vary in neutron numbers while maintaining the same number of protons.

05:01

📚 Historical Development of Atomic Models

This paragraph delves into the historical development of atomic models, starting with John Dalton's 1803 proposal of atoms as solid spheres of different sizes. The narrative progresses to JJ Thomson's 1897 'plum pudding' model, which introduced the concept of electrons within an atom. Ernest Rutherford's 1909 model is then discussed, highlighting his discovery of the nucleus and the atom's mostly empty space. The paragraph concludes with Neils Bohr's 1913 model, which introduced the idea of fixed energy shells for electrons, solving the issue of electron collapse towards the nucleus. This historical overview provides context for the evolution of our understanding of atomic structure.

10:02

🧪 Understanding Isotopes and Mass Spectra

The final paragraph discusses the concept of isotopes, which are variants of an element with different numbers of neutrons, resulting in different masses while sharing the same number of protons. It explains the use of mass spectrometry to measure the mass of isotopes, detailing the process where elements lose an electron and form a positive charge. The paragraph describes how mass-to-charge ratios (m/z) are used to determine the mass of isotopes, with the majority of ions forming a +1 charge. It explains the concept of percentage abundance, which represents the proportion of each isotope in a sample. The paragraph concludes with an example of calculating the relative atomic mass of an element using the abundance and mass of its isotopes, illustrating the process with chlorine and germanium as examples. This section provides a practical understanding of how isotopes are identified and their masses determined.

Keywords

💡Atomic Structure

Atomic structure refers to the arrangement of protons, neutrons, and electrons within an atom. In the video, Chris Harris explains that atoms consist of a nucleus containing protons and neutrons, with electrons orbiting around it. This structure is fundamental to understanding chemical properties and reactions, as it determines how atoms interact with one another.

💡Isotopes

Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. The video discusses how isotopes of an element have the same number of protons but different numbers of neutrons, leading to different atomic masses. Isotopes are important in various fields, including chemistry, physics, and geology.

💡Protons

Protons are subatomic particles found in the nucleus of an atom, carrying a positive electric charge. The video mentions that protons have a relative charge of +1 and a relative mass of 1. They are crucial in determining the element's identity and its chemical properties.

💡Neutrons

Neutrons are subatomic particles in an atom's nucleus that carry no net electric charge. According to the video, neutrons have a relative mass of 1, similar to protons, but they do not affect the electrical properties of an atom. The number of neutrons can vary among isotopes of the same element.

💡Electrons

Electrons are negatively charged subatomic particles that orbit the nucleus of an atom. The video explains that electrons have a relative charge of -1 and a much smaller relative mass, approximately 1/2000. They are responsible for chemical bonding and play a key role in chemical reactions.

💡Ions

Ions are atoms or molecules that have a net electrical charge due to the loss or gain of one or more electrons. In the video, it is mentioned that ions are formed when atoms lose or gain electrons, resulting in an unequal number of protons and electrons, which gives them a net charge.

💡Atomic Number

The atomic number, also known as the proton number, is the count of protons in the nucleus of an atom. The video explains that the atomic number is indicated by the smaller number in the element's notation and determines the element's position in the periodic table.

💡Mass Number

The mass number is the total number of protons and neutrons in an atom's nucleus. As described in the video, the mass number is the larger number associated with an element and is used to distinguish between different isotopes of that element.

💡Relative Atomic Mass

Relative atomic mass is a dimensionless value that compares the average mass of atoms of an element to 1/12 of the mass of an atom of carbon-12. The video uses this concept to explain how the average mass of an element is calculated, taking into account the abundance of its isotopes.

💡Mass Spectra

Mass spectra is a technique used to determine the mass-to-charge ratio of ions, which can be used to identify isotopes and their relative abundances. The video describes how mass spectra can be used to measure the mass of isotopes and calculate the relative atomic mass of an element.

💡Periodic Table

The periodic table is a tabular arrangement of the chemical elements, organized by atomic number, electron configuration, and recurring chemical properties. In the video, the periodic table is used as a reference to identify elements based on their atomic mass and to illustrate the distribution of elements and isotopes.

Highlights

Introduction to atomic structure and isotopes for OCR specification.

Availability of PowerPoints for purchase to aid in revision.

Explanation of the atom's composition including protons, neutrons, and electrons.

Description of the relative charges and masses of subatomic particles.

Importance of the number of protons and electrons in determining atomic structure.

Calculation method for determining the number of neutrons in an atom.

Definition and example of ions, including their formation and charge.

Explanation of ionic bonding and its role in forming stable compounds.

Introduction to isotopes, their definition, and how they differ from ions.

Discussion on the isotopes of carbon and their varying neutron counts.

Historical overview of atomic models, starting with John Dalton's spherical atoms.

JJ Thomson's plum pudding model and the discovery of the electron.

Ernest Rutherford's gold foil experiment and the discovery of the nucleus.

Niels Bohr's model of fixed energy shells and its significance.

Modern atomic model with subshells and its implications for ionization trends.

Definition of relative atomic mass and its calculation using isotopes' abundance.

Explanation of mass spectrometry and its use in measuring isotopes' mass.

Method for calculating relative atomic mass from mass spectrometry data.

Identification of elements using their relative atomic mass from the periodic table.

Conclusion and call to action for subscribing to the channel and purchasing PowerPoints.

Transcripts

[Music]

hello and welcome to this video uh this

is the OCR atomic structure and Isotopes

revision video uh my name is Chris

Harris I'm from allert tutors.com uh and

in this video like I say we're going to

go through the just give you a quick

overview of the atomic structure and

Isotopes part for the OCR specification

um the Powerpoints that I'm using here

um you can um purchase these PowerPoints

if you just click on the link in the

description box below this video be able

to get them there they' be great for

things like revision um adding to your

notes Etc you can use them um on your

phone and the tablet and the way to

school or college or anything so

there'll be um there's just another way

another bit of material for you to

revise from all right like I say these

things are based on the specification so

as you can see obviously these are the

spef spe ification points um and this

one is directly linked to the OC

specification okay so um just to remind

you as well this one's from module two

obviously this bit here okay so it

starts off looking at the atom okay so

we need to know the structure of the

atom the atom is made of protons and

neutrons as you can see in the middle

here they're really small relative to

the full size of the atom we have

negative electrons orbiting round in

shells and these take up most of the

space of an atom the charges of these

things proton is a relative charge at

plus one its mass is one relative mass

the neutron zero it's relative mass is

one this is basically just the the mass

relative to each other and electron has

got a charge of minus one uh and its

relative mass is 1 over 2,000 you can't

just put zero because electron does have

a mass it's just very very small um you

can probably remember these as uh proton

positive proton for positive charge

Neutron neutral for neg for neutral

charge so um you could probably um

remember it in that way okay obviously

in the periodic table you have your

elements and you have two numbers in

these elements here the top number uh or

sometimes it might be the other side

actually so we'll say the bigger number

the bigger number is called the mass

number uh it tells us the number of

protons and neutrons in the nucleus uh

and the smaller number tells us the it's

called the atomic or the proton number

and this basically just tells us the

number of protons in the nucleus um and

also in atoms as well it's really

important to know that the number of

protons equals the number of electrons

in atoms and if you wanted to work out

the number of neutrons all we do is you

subtract your 7 minus 3 and obviously

that will tell you the number of

neutrons in an

atom okay so let's look at ions and

Isotopes so ions are um basically atoms

that have lost or gained electrons um

and they have a different number of

electrons and protons they're not the

same unlike in atoms so for example

here's oxygen oxygen is in in group uh

six it has six electrons in its outer

shell um so to gain a full shell of

electrons um it would need an extra two

electrons to get the full eight and then

it would attract to a positive charge to

form a stable compound um we can see

oxygen here oxygen is eight protons with

a charge of plus eight eight neutrons

obviously that doesn't have a charge and

the ion has 10 electrons charge of min-2

so if we do do Min - 10 plus 8 that

gives a total charge of- two so um this

is obviously a negative charge and this

would bond to something that's

positively charged something like sodium

uh it has 11 protons charge of + 11 12

neutrons no charge 10 electrons its

charge is minus 10 obviously because

it's got one more proton than it does

electron its total charge is+ one these

two can OB you bond together and form a

much more stable compound um so that's

pretty pretty useful and you see them a

lot that's an ionic

bond right isops are a little bit

different so these are elements with the

same number of protons they have a

different number of neutrons okay so

this is going to make it um obviously a

little bit heavier each of the Isotopes

so let's have a look at these Isotopes

here these are three different types of

carbon 12 um and um three different

types of carbon isotop sorry we have

carbon 12 carbon 13 carbon 14 uh and

obviously we've got the the proton

number or the atomic number on the

bottom now what I've done is I've

written down the uh number of protons

neutrons and electrons in each one of

these

um and there's some things that we need

to point out so if you look on the top

one these things have the same number of

protons all of these do but the number

of neutrons is different if you look

we've gone from six neutrons here seven

neutrons here eight neutrons here okay

so these are called Isotopes so make

sure you'll be able to recognize

them okay we need to know about the

history of the atom as well how the atom

has developed over time so we've got

this timeline here we're going to start

way back in 1803 John Dalton he came up

with the IDE idea of spheres he said

that all atoms were spheres uh and he

just had different types of spheres

different sizes and that's basically

what he come up with so he had a first

go with it obviously we don't we know

this is not true now um but back then it

was accepted and until we had in

1897 so um just over 90 years later we

had JJ Thompson uh he had another go and

he kind of amended John Dalton's idea uh

and came up with a new model uh

basically he discovered the electron uh

he said the atom wasn't solid uh and was

made up of other particles and he called

it the plum pudding model so he said

that he had negative uh negative

electrons which are these yellow circles

here and we had the positive pudding bit

so um I have no idea what a plum P would

look like but obviously it must look

something like this um so he basically

came up with this idea and he tried to

explain um his model obviously in a more

um less abstract Way by coming up with

the word plum pudding

uh a little bit later on 1909 Ernest

Rutherford okay so he developed

Thompson's idea it wasn't so much of a

gap now he discovered the nucleus and he

said that actually this nucleus is

really small uh and it was positively

charged and he he basically said it was

really small compared to the rest of the

atom he said it was mainly empty space

and it was made of some negative Cloud

he said so it was just like a cloud of

negative stuff around a positive um very

small nucleus and he had some evidence

actually to back this up um he used a

gold leaf experiment and basically what

he did is he fired alpha particles at a

thin bit of gold leaf most of them went

through um which suggested that most of

the at was empty space um some of them

were deflected which means they were

kind of because alpha particles were

positively charged they deflected away

from the nucleus that told them it must

have been a positive nucleus and some

very very very few bounced straight back

towards where the alpha part were being

fired at and he but basically suggested

that this nucleus was absolutely tiny

because not many of them were actually

being completely uh fired back at him so

basically that was his evidence and he

used this gold leaf

experiment uh a little bit later on 1913

Neils B right he said well actually

there's an issue with this there's a

problem he said how can you have a cloud

of electrons around a positive nucleus

The Cloud of electrons just collapse cuz

obviously nucleus was positive and the

electrons were negative so they would

attract each other it just collapse into

the atom so what he said was he said

actually um we must have something else

and not something else was fixed energy

shells so Neil's B came up with the idea

of energy shells so this was the model

that we getting bit little bit more

familiar with now so and actually he

could prove it he said when the EM

radiation is absorbed so this is

electromagnetic radiation the electrons

can move between the shells and when

they do that they emit this radiation

when the electrons move down to lower

shells and he measured um this um this

kind of emission that was coming from

the atoms and the only way you could

describe this was using this shell

Theory you couldn't do it with a cloud

model so um that's pretty uh that's

pretty

important okay the atomic model today

obviously electrons don't have the same

energy in the shells obviously nowadays

we now we've got now we know that we've

got subshells um and this basically

explains the ionization Trends okay so

the trend

um which we'll see um later on in this

in this module okay so obviously we know

got subshells like P SD subshells

Etc okay your definitions right you

really do need to know these definitions

apart from this bottom one in the red

but you do need to know all the rest of

them so we've got let's have a look at

this blue one this is called the

relative atomic mass okay or the a

basically this is the weighted mean mass

of an atom uh of an element compared to

1 12th of the mass of a carbon 12 atom

so um this is basically the uh the uh

the mass of something like an atom for

example the relative isotopic mass this

is the mass of an atom of an isotope

compared to 1 12th of the mass of an

atom of carbon 12 so this is basically

the mass of an isotope that makes it up

notice they're kind of they're very

similar in terms of um 112th of the mass

of at of carbon 12 very very important

and Rel to molecular mass um this might

be a bit useful you don't have to

remember this definition um for OCR but

it's just the mean mass of a molecule

compared to 1 12th of the mass of an

atom carbon 12 basically everything was

measured uh against carbon 12 okay so um

that was like the reference uh element

that they used hence the word

relative okay so let's look at Mass

Spectra so Mass Spectra is a way in

which we can measure the um the mass of

Isotopes in an element and just want to

kind of walk you through the the graph

and show you what we've got here okay so

looking at the bottom here this is

called the MZ the MZ is the mass to

charge ratio um basically this is the

mass of the isotope divided by its

charge now when it goes to a mass

spectrometer the elements lose an

electron and and when they lose this

electron obviously they form a positive

charge now most of the time the vast

majority of the time only one electron

is knocked off so we only form one plus

charge so when we do the mass of the

isotop divided by one we just get

literally the mass of the isotope so

most of it is plus one charge and this

is basically the same as the isotopic

mass so for example 37 is the MZ here we

can basically assume that is the mass of

the isotop as well or the relative mass

along theide here's percentage abundance

this is given as a percentage uh

abundance of the isotope in the sample

so obviously abundance is the amount of

something so the higher the abundance

the more of it you got um sometimes it's

shown as a percentage in which case it

be out of 100 sometimes it might be a

nominal value so it'll just be called

relative abundance in which case you

just add up all the Isotopes and that'll

tell you obviously what to divide it by

which you'll show see in a minute okay

so the must add up to give 100 there we

go 75 we only got two isops here 75% 25%

so they add up to

100 okay this Spectra like I say shows

two isotopes we've got one element but

two isops 75% of isops with a mass of 35

20 25% of the Isotopes with a mass of 37

so this is assuming they all have a one

plus charge obviously that's the

Assumption we're taking and most of them

will and so from this actually we can

work out the relative atomic mass and

we're going to have a look at that

next okay so let's have a look how we

can work this out so the relative atomic

mass can be worked out by taking the

abundance of a multiplied by the m to

charge of a plus the abundance of B

Times by the mass the charge of B Etc so

here we've only got two ice TOS but if

you had three or four or five you

literally just repeat these bits and

just keep adding them up divide it by

the total abundance now in this case the

abundance is percentage so it's out of

100 but yours might not be and yours

might be a relative abundance in which

case you just add the total abundance

for each ice toop and put that number at

the bottom there in this case we're

using percentage so relative uh relative

atomic mass 75 * 35 which is that time

that 25 * 37 which is 25 * 37 multiply

them two divid it by 100 cuz it's a

percentage abundance and we should get

35.5 we can use the periodic table and

we can identify the element as chlorine

if you look at the period table you

should see the mass that has 35.5 is

chlorine so pretty useful

actually right this is a different way

of doing it uh this is just using one

with a table again we just got Isotopes

and we've got abundance uh you see we've

got a few isops in this one um and we

got the abundance of each again it's out

of a percentage so let's have a look

relative atomic Mass 70 * 20.5 time uh

plus 72 + 27.4 blah blah blah right all

the way along basically we're just

multiplying these two that times that

plus that times that plus that times

that Etc all the way along divid it by

100 because it's a percentage abundance

so that's the total amount now if we put

that in our calculator we should get the

answer to be

72.6 and again if we look in the

periodic table we should be able to

identify the element as germanium or GE

so you can check that out and have a

look on the periodic

table and that's it that is um the

little quite small topic on atomic

structure and isops um please remember

to subscribe to my channel if you just

click on um the middle button uh right

now um and remember you can purchase

these uh PowerPoints if you like from

the link in the description box just

click on that link there and you can get

a hold of them great for vision all

right that's it now bye-bye