ESTADOS DE OXIDACIÓN. REGLAS PARA ASIGNAR NUMEROS O ESTADOS DE OXIDACION

ARRIBA LA CIENCIA

23 Aug 202015:14

Summary

TLDRThe video introduces an easy-to-understand approach to learning oxidation states in chemistry. It begins by explaining the concept of oxidation numbers, which are crucial for naming inorganic compounds. The video covers five essential rules for assigning oxidation numbers, including how elements in a monoatomic state have an oxidation number of zero, and how hydrogen and oxygen generally have oxidation numbers of +1 and -2, respectively. The rules are applied to various examples, emphasizing their importance in understanding compound neutrality. The lesson is designed to be simple and useful for upcoming nomenclature topics.

Takeaways

😀 Oxidation states are essential for understanding the naming of inorganic compounds.
⚖️ Oxidation states are always integers, typically ranging from 1 to 7, and can be positive or negative.
🧠 Rule 1: The oxidation state of a monoatomic element is always zero when it is uncombined.
🔋 Rule 2: For group 1, 2, and 3 elements, the oxidation states are +1, +2, and +3 respectively when they are bonded.
🔑 Hydrogen generally has an oxidation state of +1, but it is -1 when combined with a metal (hydrides).
🌬️ Oxygen typically has an oxidation state of -2, except when combined with fluorine (+2) or in peroxides (-1).
⚙️ Rule 5: In compounds where the above rules don't apply, the oxidation states are assigned based on neutrality—positive and negative charges should cancel out to zero.
💡 To determine an unknown oxidation state, balance the known oxidation states of other elements in the compound.
🔍 Example: In NaCl, sodium (Na) has an oxidation state of +1, and chlorine (Cl) has -1, balancing each other out.
🧪 Correct application of oxidation states is essential for compound neutrality, with positive and negative charges always balancing.

Q & A

What are oxidation states?
-Oxidation states represent the net charge an atom would have if electrons were completely transferred to the more electronegative atom in a bond. This concept helps in understanding how compounds are named and their chemical behavior.
What are the typical oxidation states for elements in the periodic table?
-Elements in groups 1, 2, and 3 typically have oxidation states of +1, +2, and +3, respectively. For example, sodium has +1, calcium has +2, and aluminum has +3.
What is the oxidation state of an element in its monatomic form?
-The oxidation state of an element in its monatomic form (e.g., sodium or oxygen molecules) is always zero.
How do you assign oxidation states to hydrogen?
-Hydrogen usually has an oxidation state of +1 when bonded with nonmetals. However, when bonded with metals, as in hydrides, it has an oxidation state of -1.
What are the rules for assigning oxidation states to oxygen?
-Oxygen typically has an oxidation state of -2, except when bonded to fluorine (where it is +2) or in peroxides (where it is -1).
What is the sum of oxidation states in a neutral molecule?
-In a neutral molecule, the sum of the oxidation states of all atoms must equal zero to ensure that the molecule is electrically neutral.
How do you calculate the oxidation state of chlorine in NaCl?
-In NaCl, sodium has an oxidation state of +1, so chlorine must have an oxidation state of -1 to balance the charges and maintain a neutral molecule.
Why is it important to balance oxidation states in molecules?
-Balancing oxidation states ensures that the total charges of a molecule or compound are neutral, following the rule that compounds must have no overall charge unless they are ions.
How does oxidation state assignment help with chemical nomenclature?
-Understanding oxidation states is crucial for naming inorganic compounds correctly, as it indicates the charge of each element and helps identify the compound's structure.
What is a key takeaway for mastering oxidation states?
-A solid grasp of the rules for assigning oxidation states, especially for common elements like oxygen and hydrogen, is essential for understanding chemical reactions and naming compounds.

Outlines

00:00

📚 Introduction to Oxidation Numbers

The video starts with a warm welcome, encouraging viewers to subscribe. It introduces the concept of oxidation numbers (or oxidation states), explaining that they represent the net charge that an atom would have if the electrons were assigned to the more electronegative atom. Understanding oxidation numbers is crucial for naming inorganic compounds. Key points include that oxidation numbers are always integers and can be positive or negative. The paragraph also introduces the five rules for assigning oxidation numbers, beginning with the first rule: elements in their pure atomic or molecular state have an oxidation number of zero.

05:01

🔢 The Oxidation Number Rules for Groups 1, 2, and 3

This paragraph explains the second rule, focusing on the oxidation numbers of elements in groups 1, 2, and 3 of the periodic table. When elements from these groups are bonded to others, their oxidation states are +1, +2, and +3, respectively. The example of sodium (group 1) and calcium (group 2) illustrates this rule, with sodium having an oxidation number of +1 and calcium +2 when bonded. The importance of understanding these oxidation numbers is stressed, particularly in relation to different chemical compounds.

10:03

🧪 Hydrogen Oxidation Numbers in Various Compounds

The third rule discussed focuses on hydrogen, which typically has an oxidation number of +1 in most compounds. However, when hydrogen is bonded with a metal (forming hydrides), its oxidation number becomes -1. Several examples are provided to illustrate how hydrogen's oxidation state changes depending on whether it is bonded to a metal or a non-metal. The paragraph emphasizes how crucial hydrogen's role is, as it appears in many compounds.

15:03

🌬️ Oxygen and Its Special Oxidation Rules

This section discusses the fourth rule, which pertains to oxygen. Oxygen almost always has an oxidation number of -2, except in two specific cases: when bonded to fluorine (where it has a +2 oxidation state) or in peroxides (where it has an oxidation number of -1). These exceptions are explained in detail, but the general rule that oxygen is -2 in most compounds is highlighted as being essential.

🔧 Assigning Oxidation Numbers to Balance Charges

The fifth and final rule is introduced, which deals with assigning oxidation numbers to other elements to ensure that the overall charge of the molecule remains neutral. This rule is important when none of the previous rules apply. Several examples are provided, showing how to balance oxidation numbers in compounds by ensuring that the sum of the positive and negative charges equals zero. The sodium chloride (NaCl) and calcium bromide (CaBr₂) examples are used to demonstrate how oxidation numbers are assigned to balance molecular charges.

🔍 Complex Oxidation Number Calculations

This paragraph delves into more complex examples where multiple atoms of an element are involved. The process of calculating oxidation numbers for compounds with multiple atoms of an element, such as aluminum and sulfur compounds, is explained in detail. The importance of ensuring that the total positive and negative charges balance out is reiterated. The calculations help clarify how to determine the correct oxidation numbers by using known rules for each element and adjusting for the overall charge neutrality.

💡 Practical Example: Potassium Dichromate

Here, the oxidation number calculation for potassium dichromate (K₂Cr₂O₇) is explored. The paragraph walks through assigning oxidation numbers to potassium (+1), oxygen (-2), and chromium (determined through calculations) to balance the molecule. The process involves breaking down the oxidation number of chromium based on the charges of potassium and oxygen, demonstrating how the overall charge neutrality is achieved. This example highlights the complexities that can arise in oxidation number assignments for more complicated compounds.

🏆 Conclusion and Importance of Mastering Oxidation Numbers

The final paragraph emphasizes the importance of mastering oxidation numbers, as they are foundational to understanding chemical nomenclature and reactions. The speaker encourages viewers to review the video if necessary to grasp the topic fully. Oxidation numbers will be crucial in the upcoming sections on naming compounds, making it essential to practice and become comfortable with these calculations. The video ends with gratitude for the audience's attention and motivation to continue learning.

Mindmap

Keywords

💡Oxidation Numbers

Oxidation numbers represent the charge that an atom would have if electrons were fully transferred in a bond. In the video, they are central to understanding how elements interact in compounds. For instance, the sodium (Na) atom in a compound would typically have an oxidation number of +1, which helps in determining the charge balance within the compound.

💡Monatomic Elements

Monatomic elements are elements that exist as single atoms, such as sodium (Na) or calcium (Ca), when not bonded to others. The video explains that these elements have an oxidation number of zero when in their pure elemental state. For example, the oxidation number of sodium (Na) would be zero when it is not part of a compound.

💡Groups in the Periodic Table

The periodic table is divided into groups, which are vertical columns where elements share common properties. The video explains that elements in Group 1 have an oxidation number of +1, Group 2 elements have an oxidation number of +2, and Group 3 elements have an oxidation number of +3 when bonded in compounds. For example, calcium in Group 2 typically has an oxidation number of +2.

💡Hydrogen

Hydrogen generally has an oxidation number of +1 when bonded with non-metals and -1 when bonded with metals, like in hydrides. The video emphasizes hydrogen's frequent presence in compounds and its variable oxidation states depending on the element it bonds with, such as when it forms hydrides with metals.

💡Oxygen

Oxygen usually has an oxidation number of -2 in most compounds, except in peroxides where it is -1 and when bonded with fluorine where it can be +2. This rule is referred to as a 'golden rule' in the video because of oxygen's frequent presence in compounds and its importance in determining oxidation numbers.

💡Peroxides

Peroxides are compounds where oxygen has an oxidation number of -1, different from its usual -2 state. The video highlights peroxides as one of the few exceptions to the general rule that oxygen is always -2 in compounds. An example from the video is hydrogen peroxide (H₂O₂), where oxygen has an oxidation number of -1.

💡Fluorine

Fluorine is a highly electronegative element, always having an oxidation number of -1 in its compounds. The video explains that when oxygen bonds with fluorine, oxygen's oxidation state changes from -2 to +2, making fluorine an important exception in redox reactions.

💡Neutral Molecules

A neutral molecule is one where the total sum of all oxidation numbers in the molecule equals zero. The video frequently emphasizes the importance of balancing oxidation numbers so that the overall charge of a compound remains neutral. For example, sodium chloride (NaCl) balances the +1 of sodium with the -1 of chlorine to form a neutral compound.

💡Electron Transfer

Electron transfer refers to the movement of electrons between atoms, which is central to oxidation-reduction (redox) reactions. The video explains that oxidation numbers are used to track electron transfers in reactions, with electrons typically being assigned to the more electronegative atom, such as when oxygen pulls electrons towards itself in compounds.

💡Rules for Assigning Oxidation Numbers

The video outlines five key rules for determining oxidation numbers, such as the rule that elements in their pure form have an oxidation number of zero, and that hydrogen and oxygen follow specific patterns unless in exceptional cases like peroxides. These rules are fundamental for understanding how oxidation states are assigned in chemical compounds.

Highlights

Introduction to oxidation states, their importance in naming inorganic compounds.

Oxidation states are whole numbers, typically ranging from 1 to 7, with charges that can be positive or negative.

Monoatomic elements have an oxidation state of zero, including sodium, aluminum, and calcium.

The oxidation state of diatomic elements like oxygen (O2) or triatomic elements like ozone (O3) is also zero.

Oxidation states for group 1 elements are always +1, group 2 elements are always +2, and group 3 elements are +3.

Hydrogen has an oxidation state of +1 when combined with non-metals, but -1 when combined with metals in hydrides.

Oxygen generally has an oxidation state of -2, except when combined with fluorine (+2) or in peroxides (-1).

When assigning oxidation numbers, the sum of the oxidation states in a neutral compound must equal zero.

In sodium chloride (NaCl), sodium has an oxidation state of +1, and chlorine has an oxidation state of -1.

In calcium bromide (CaBr2), calcium has an oxidation state of +2, while bromine has an oxidation state of -1.

In aluminum oxide (Al2O3), aluminum has an oxidation state of +3, and oxygen has an oxidation state of -2.

The rule for hydrogen in most compounds is that its oxidation state is +1.

The oxidation state of sulfur in sulfuric acid (H2SO4) is +6.

Potassium typically has an oxidation state of +1, and oxygen is -2 in most compounds.

Assigning oxidation numbers can be challenging, but understanding the rules and practicing will make it easier.