atomic structure
,C1 Atomic Structure — Study Notes
1. Atoms and Elements
● All substances are made of tiny particles called atoms.
● There are about 100 different types of atoms found naturally on Earth.
● An element is a substance made of only one type of atom.
● An atom is the smallest part of an element that can exist.
● Because there are ~100 types of atoms, there are ~100 elements.
2. Properties of Elements
● Elements can have very different properties.
● Metals (e.g. gold, silver, copper, chromium):
○ Usually shiny
○ Solid at room temperature
● Non-metals (e.g. oxygen, nitrogen, chlorine, argon):
○ Often gases at room temperature
3. Chemical Symbols
● Elements have chemical symbols that are the same worldwide.
● Symbols represent atoms of elements:
○ O = oxygen atom
○ Na = sodium atom
● Some symbols come from Latin names:
○ Sodium (Na) → natrium
○ Gold (Au) → aurum
○ Lead (Pb) → plumbum
○ Potassium (K) → kalium
4. The Periodic Table
● The periodic table lists all known elements.
● Elements are arranged in groups (columns).
● Elements in the same group have similar chemical properties.
● A bold “staircase” line divides:
○ Metals (left)
○ Non-metals (right)
● Metalloids (semi-metals) lie next to the line and have mixed properties:
○ Examples: silicon (Si), germanium (Ge)
5. Compounds
● Most substances are compounds, not elements.
, ● A compound contains two or more different types of atoms chemically bonded.
● Example: Water (H₂O)
○ Always has 2 hydrogen atoms for every 1 oxygen atom
● If there is no number after a symbol, it means 1 atom.
● Compounds are held together by chemical bonds, which are hard to break.
● Compounds are hard to separate because atoms are chemically bonded.
6. Molecules
● A molecule is a group of two or more atoms bonded together.
● Molecules can be:
○ Elements (e.g. O₂)
○ Compounds (e.g. H₂O, CO₂)
7. Structure of an Atom
● An atom consists of:
○ A tiny central nucleus
○ Electrons moving around the nucleus
● The nucleus is very small compared to the whole atom.
8. Key Exam Points
● Elements = one type of atom
● Compounds = more than one type of atom
● Chemical formulas show the ratio of atoms
● Elements mixed physically can be separated easily
● Compounds are difficult to separate due to chemical bonds
C1.2 Chemical Equations — Study Notes
1. Chemical Reactions
● A chemical reaction happens when atoms are rearranged.
● No atoms are created or destroyed in a chemical reaction.
● Chemical equations show:
○ Reactants → substances you start with
○ Products → new substances formed
2. Word Equations and Symbol Equations
● Word equations use names of substances:
○ hydrogen + oxygen → water
● Symbol equations use chemical formulas:
, ○ H₂ + O₂ → H₂O
● Symbol equations show how much of each substance is involved.
3. Balanced Symbol Equations
● A balanced equation has the same number of each type of atom on both sides.
● This is essential because of the Law of Conservation of Mass.
● You can check if an equation is balanced by counting atoms on each side.
● You must NEVER change a chemical formula to balance an equation.
● You balance equations by adding numbers in front of formulas (coefficients).
Example (hydrogen and oxygen):
● Unbalanced: H₂ + O₂ → H₂O
● Balanced: 2H₂ + O₂ → 2H₂O
4. Law of Conservation of Mass
● Total mass of reactants = total mass of products
● This law always applies in chemical reactions.
5. Reactions Involving Gases
● In open containers, mass can appear to change:
○ Loss in mass: gas escapes into the air (e.g. CO₂)
○ Gain in mass: gas from air reacts (e.g. oxygen)
● The law of conservation of mass still applies — the gas just isn’t being measured.
Examples:
● Calcium carbonate heated:
○ CaCO₃ → CaO + CO₂
○ Mass appears to decrease because CO₂ escapes
● Copper heated in air:
○ Gains mass because it reacts with oxygen
6. State Symbols
State symbols give extra information about substances:
Symbo Meaning
l
(s) solid
,C1 Atomic Structure — Study Notes
1. Atoms and Elements
● All substances are made of tiny particles called atoms.
● There are about 100 different types of atoms found naturally on Earth.
● An element is a substance made of only one type of atom.
● An atom is the smallest part of an element that can exist.
● Because there are ~100 types of atoms, there are ~100 elements.
2. Properties of Elements
● Elements can have very different properties.
● Metals (e.g. gold, silver, copper, chromium):
○ Usually shiny
○ Solid at room temperature
● Non-metals (e.g. oxygen, nitrogen, chlorine, argon):
○ Often gases at room temperature
3. Chemical Symbols
● Elements have chemical symbols that are the same worldwide.
● Symbols represent atoms of elements:
○ O = oxygen atom
○ Na = sodium atom
● Some symbols come from Latin names:
○ Sodium (Na) → natrium
○ Gold (Au) → aurum
○ Lead (Pb) → plumbum
○ Potassium (K) → kalium
4. The Periodic Table
● The periodic table lists all known elements.
● Elements are arranged in groups (columns).
● Elements in the same group have similar chemical properties.
● A bold “staircase” line divides:
○ Metals (left)
○ Non-metals (right)
● Metalloids (semi-metals) lie next to the line and have mixed properties:
○ Examples: silicon (Si), germanium (Ge)
5. Compounds
● Most substances are compounds, not elements.
, ● A compound contains two or more different types of atoms chemically bonded.
● Example: Water (H₂O)
○ Always has 2 hydrogen atoms for every 1 oxygen atom
● If there is no number after a symbol, it means 1 atom.
● Compounds are held together by chemical bonds, which are hard to break.
● Compounds are hard to separate because atoms are chemically bonded.
6. Molecules
● A molecule is a group of two or more atoms bonded together.
● Molecules can be:
○ Elements (e.g. O₂)
○ Compounds (e.g. H₂O, CO₂)
7. Structure of an Atom
● An atom consists of:
○ A tiny central nucleus
○ Electrons moving around the nucleus
● The nucleus is very small compared to the whole atom.
8. Key Exam Points
● Elements = one type of atom
● Compounds = more than one type of atom
● Chemical formulas show the ratio of atoms
● Elements mixed physically can be separated easily
● Compounds are difficult to separate due to chemical bonds
C1.2 Chemical Equations — Study Notes
1. Chemical Reactions
● A chemical reaction happens when atoms are rearranged.
● No atoms are created or destroyed in a chemical reaction.
● Chemical equations show:
○ Reactants → substances you start with
○ Products → new substances formed
2. Word Equations and Symbol Equations
● Word equations use names of substances:
○ hydrogen + oxygen → water
● Symbol equations use chemical formulas:
, ○ H₂ + O₂ → H₂O
● Symbol equations show how much of each substance is involved.
3. Balanced Symbol Equations
● A balanced equation has the same number of each type of atom on both sides.
● This is essential because of the Law of Conservation of Mass.
● You can check if an equation is balanced by counting atoms on each side.
● You must NEVER change a chemical formula to balance an equation.
● You balance equations by adding numbers in front of formulas (coefficients).
Example (hydrogen and oxygen):
● Unbalanced: H₂ + O₂ → H₂O
● Balanced: 2H₂ + O₂ → 2H₂O
4. Law of Conservation of Mass
● Total mass of reactants = total mass of products
● This law always applies in chemical reactions.
5. Reactions Involving Gases
● In open containers, mass can appear to change:
○ Loss in mass: gas escapes into the air (e.g. CO₂)
○ Gain in mass: gas from air reacts (e.g. oxygen)
● The law of conservation of mass still applies — the gas just isn’t being measured.
Examples:
● Calcium carbonate heated:
○ CaCO₃ → CaO + CO₂
○ Mass appears to decrease because CO₂ escapes
● Copper heated in air:
○ Gains mass because it reacts with oxygen
6. State Symbols
State symbols give extra information about substances:
Symbo Meaning
l
(s) solid
