Lewis Dot Structures
Summary
TLDRProfessor Dave's tutorial on Lewis dot structures enlightens viewers on the representation of atoms and their valence electrons, crucial for understanding covalent bonding. The video explains how to depict atoms, their coordination sites, and the formation of covalent bonds, including single, double, and triple bonds. It also touches on formal charges and the tendency of atoms like carbon, nitrogen, oxygen, and fluorine to form specific numbers of bonds. The tutorial is designed to enhance comprehension of molecular structures and chemical bonding.
Takeaways
- 🔬 Lewis dot structures represent atoms and their valence electrons in a chemical context.
- 🌐 Atoms are depicted by their chemical symbols, with valence electrons shown as dots around them.
- 📊 Carbon, for example, has four valence electrons and is represented with four dots in its outermost shell.
- 🔄 The drawing of valence electrons follows a specific order: place one electron per coordination site before pairing them up.
- 👫 Elements in the same group have similar Lewis dot symbols due to the same number of valence electrons.
- 🤝 In Lewis dot structures for molecules, unpaired electrons from different atoms can form covalent bonds, represented as lines.
- 🔗 The number of valence electrons an atom has influences how many bonds it forms, such as carbon forming four bonds.
- 💠 Atoms can form single, double, or triple bonds, with the latter being the shortest in length.
- 🎯 Formal charges may appear in Lewis dot structures when an atom contributes a different number of electrons than its typical valence.
- 🌀 Larger atoms like phosphorus and sulfur can form more than four covalent bonds, aiming to fill their outermost shell with eight electrons.
Q & A
What is the purpose of learning how to draw Lewis dot structures?
-The purpose of learning how to draw Lewis dot structures is to visually represent the valence electrons of atoms and how they form covalent bonds with other atoms, which is crucial for understanding the structure of molecules.
How are valence electrons represented in a Lewis dot structure?
-Valence electrons are represented as dots around the chemical symbol of an atom. For example, carbon, which has four valence electrons, is represented with four dots around the 'C' symbol.
Why do we assume there are four coordination sites for small atoms like carbon?
-We assume there are four coordination sites for small atoms like carbon because that is the number needed for such atoms to fill their outermost shell, or octet, by forming covalent bonds.
How do you draw the valence electrons for an atom like carbon?
-For carbon, you first place one dot in each coordination site before pairing them up, resulting in a structure that looks like this: C:..., not like this: C::.
What is a covalent bond in the context of Lewis dot structures?
-A covalent bond in Lewis dot structures is represented by a line between two atoms, indicating that unpaired electrons from each atom have combined to form a bond, which always contains two electrons.
What is a sigma bond and how does it differ from a pi bond?
-A sigma bond is the first covalent bond formed between two atoms. A pi bond is the second bond in a double bond or the second and third bonds in a triple bond. Pi bonds are represented in Lewis structures as lines that form a 'sideways' bond.
Why do single, double, and triple bonds differ in length?
-Single covalent bonds are the longest because they consist of one pair of electrons between the atoms. Double bonds are shorter because they have two pairs of electrons closer together, and triple bonds are the shortest due to three pairs of electrons being even closer.
What is a formal charge and how does it relate to Lewis dot structures?
-A formal charge is the charge an atom appears to have in a Lewis dot structure when the number of electrons it is contributing differs from its typical valence. It is calculated by the formula: Formal charge = (Valence electrons of the atom) - (Non-bonding electrons) - (1/2 × Bonding electrons).
Why does nitrogen in ammonia have a neutral charge while in the ammonium ion it has a formal positive charge?
-In ammonia (NH3), nitrogen contributes all five of its valence electrons, one per covalent bond, and has no formal charge. In the ammonium ion (NH4+), nitrogen contributes four electrons to the structure, one less than its typical valence, resulting in a formal positive charge.
How do larger atoms like phosphorus and sulfur form more than four covalent bonds?
-Larger atoms like phosphorus and sulfur can have more than four valence electrons and thus can form more than four covalent bonds. They can expand their octet by utilizing d-orbitals to accommodate more than eight electrons, a phenomenon known as 'expanded octet.'
Outlines
🔬 Introduction to Lewis Dot Structures
Professor Dave introduces the concept of Lewis dot structures, explaining how they represent atoms and their valence electrons. The paragraph details the process of drawing these structures, starting with the chemical symbol for an atom and then surrounding it with dots representing valence electrons. It emphasizes the importance of placing electrons in coordination sites before pairing them up, and how elements in the same group will have similar Lewis dot symbols due to the same number of valence electrons. The paragraph also explains the formation of covalent bonds, where unpaired electrons from different atoms combine, represented by a line instead of dots, and the preference of atoms to form bonds based on their valence electron count.
Mindmap
Keywords
💡Lewis dot structures
💡Valence electrons
💡Covalent bonds
💡Sigma bond
💡Pi bond
💡Formal charge
💡Octet rule
💡Hydrogen
💡Phosphorus and Sulfur
💡Polyatomic ion
Highlights
Introduction to drawing Lewis dot structures for covalent bonding.
Representing an atom by its chemical symbol in Lewis dot structures.
Drawing valence electrons as dots around the atom for Lewis dot structures.
Carbon's electron configuration and its representation in Lewis dot structures.
Assumption of four coordination sites for small atoms like carbon.
Procedure for drawing valence electrons, starting with unpaired electrons.
Similarity in Lewis dot symbols for elements within the same group.
Drawing Lewis dot structures for molecules by pairing unpaired electrons.
Covalent bonds represented as lines between atoms in Lewis dot structures.
Electrons in Lewis dot structures are either in covalent bonds or lone pairs.
The number of valence electrons dictates the number of bonds an atom tends to form.
Tendency of carbon to form four bonds, nitrogen three, oxygen two, and fluorine one.
Explanation of sigma and pi bonds in covalent bonding.
Length differences between single, double, and triple covalent bonds.
Formal charge in Lewis dot structures due to deviation from typical valence.
Example of nitrogen's formal charge in ammonia and ammonium ion.
Atoms' desire to fill their octet with eight electrons in Lewis dot structures.
Hydrogen's unique requirement of only two electrons to fill its shell.
Larger atoms like phosphorus and sulfur can make more than four covalent bonds.
Encouragement to practice drawing valence electrons and combining unpaired ones.
Comprehension check and invitation to subscribe for more tutorials.
Transcripts
professor Dave here, let's learn how to draw Lewis dot structures
we've learned about how ions come together to form ionic compounds but much more
interesting is the way atoms form networks of covalent bonds. in order to
talk about this we're going to have to learn how to draw Lewis dot structures
when we draw these we will represent an atom by its chemical symbol. here's
carbon. we then draw that atom's valence electrons as dots around the atom. carbon is
one 1s2 2s2 2p2 so that's four electrons in the outermost shell, which
you can also tell by counting over from the left
for carbon and other small atoms we assume that there are four coordination
sites that can accommodate electrons or bonds because this is how carbon can
fill its octet, or its
outermost shell. when we draw the valence electrons we put one in each
coordination site first before pairing them up so carbon will look like this
not like this
elements in the same group will have similar looking lewis dot symbols
because they have the same number of valence electrons. now to draw a lewis dot
structure for a molecule just draw each atom with all of its valence electrons
unpaired electrons from two different atoms can come together to make covalent
bonds. when that happens instead of two dots we make a line. this is a covalent
bond which always contains two electrons. for our purposes here we can assume that
electrons need to be paired so a good lewis dot structure will have all the
electrons either inside covalent bonds or in lone pairs. the number of valence
electrons an atom has dictates how many bonds it tends to form. carbon likes to
make four bonds. nitrogen, with five valence electrons likes to have three
bonds and one lone pair. oxygen likes to have two bonds and two lone pairs. and
fluorine likes to have one bond and three lone pairs. when two atoms have one
covalent bond between them we call that a sigma bond, but atoms can have double
or even triple bonds. look at carbon dioxide. after we make a sigma bond
between the atoms there are still unpaired electrons. if adjacent atoms
each have unpaired electrons they can become another covalent bond. the second
covalent bond in a double bond is called a pi bond. the second and third bonds in
a triple bond are also pi bonds. single covalent bonds are the longest, double
bonds are a little shorter, and triple bonds are shorter still. more on these
later. sometimes an atom in a lewis dot structure will have a formal charge. this
happens if the number of electrons an atom is contributing to a lewis dot
structure is different from its typical valence. nitrogen has five valence
electrons so in ammonia
where it contributes those 5, 1 per covalent bond plus the lone pair, it will
be a neutral nitrogen atom. for the ammonium ion, nitrogen is now
contributing four electrons to the lewis dot structure, one per bond. that's one
less than its typical valence and one fewer negatively charged particles means
the nitrogen will have a formal positive charge. that makes this a polyatomic ion
these elements want to fill their octet by having eight electrons around them
filling n=2 shell. hydrogen is very small so that only needs two to
fill the n=1 shell, and larger atoms like phosphorus and sulfur can
make five or six covalent bonds. just draw valence electrons and start
combining unpaired ones. let's check comprehension
thanks for watching, subscribe to my channel for more tutorials and as always feel free to email me
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