Chemical Equations and Formulas

Balancing chemical equations is an essential skill in chemistry. It ensures that the number of atoms of each element is the same on both sides of the equation.

Example: The balanced equation for the formation of water is 2H₂ + O₂ → 2H₂O

Students must learn important chemical formulas, such as:

• Carbon dioxide (CO₂)
• Water (H₂O)
• Oxygen gas (O₂)
• Hydrogen gas (H₂)
• Nitrogen gas (N₂)
• Ammonia (NH₃)
• Hydrochloric acid (HCl)
• Sulfuric acid (H₂SO₄)

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Mixtures consist of different substances, some chemically bonded and some not. There are various methods for separating mixtures:

1. Distillation: Separates substances based on boiling point
2. Evaporation: Removes the liquid component
3. Filtration: Separates large solid particles from a liquid
4. Fractional distillation: Separates substances with different boiling points

Vocabulary: Mixture - A combination of different substances, some chemically bonded and some not.

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Atomic Models and Structure

The understanding of atomic structure has evolved over time, with several key models:

1. Plum Pudding Model: Proposed by J.J. Thomson, this model suggested that electrons were embedded in a positive "pudding."

2. Rutherford's Nuclear Model: Based on the gold foil experiment, this model proposed a small, dense, positively charged nucleus surrounded by electrons.

3. Bohr Model: Introduced the concept of electron shells orbiting the nucleus.

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Example: The Rutherford-Marsden experiment involved firing alpha particles (helium nuclei) at a thin gold foil, leading to the discovery of the nucleus.

Periodic Table Structure

The periodic table is organized into groups (vertical columns) and periods (horizontal rows). The group number indicates the number of electrons in the outer shell, while the period number shows the number of electron shells.

Example: Sodium (Na) has 11 protons and electrons, with 2 electrons in the first shell, 8 in the second, and 1 in the third.

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Ions are formed when atoms gain or lose electrons. Metals typically form positive ions by losing electrons, while non-metals form negative ions by gaining electrons.

Definition: An ion is an atom that has gained or lost electrons, resulting in a net electrical charge.

Periodic Table History and Groups

The periodic table has evolved over time, with key contributions from scientists like Newlands and Mendeleev. The modern periodic table is organized by atomic number and electron configuration.

Important groups in the periodic table include:

• Group 1: Alkali metals
• Group 2: Alkaline Earth metals
• Group 7: Halogens
• Group 0: Noble gases

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Noble gases have a full outer shell of electrons, making them very unreactive. They are used in applications such as balloons and neon lights.

Halogens (Group 7) are highly reactive non-metals that exist as diatomic molecules. They become less reactive as you move down the group.

Example: Fluorine (F₂) is more reactive than chlorine (Cl₂), which is more reactive than bromine (Br₂).

Alkali Metals and States of Matter

Alkali metals (Group 1) are highly reactive and must be stored in oil to prevent reaction with air or water. They react vigorously with water to form metal hydroxides.

Example: Sodium + Water → Sodium Hydroxide + Hydrogen gas

The states of matter (solid, liquid, and gas) and the processes of changing between them (melting, freezing, evaporating, and condensing) are important concepts in chemistry.

Vocabulary:

• Melting: The process of a solid changing to a liquid
• Freezing: The process of a liquid changing to a solid
• Evaporating: The process of a liquid changing to a gas
• Condensing: The process of a gas changing to a liquid

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Chemical Bonding

Chemical bonding is a fundamental concept in chemistry, with two main types:

1. Ionic Bonding: The transfer of electrons from a metal to a non-metal.

Example: Magnesium Oxide (MgO) formation involves magnesium losing two electrons and oxygen gaining two electrons.

2. Covalent Bonding: The sharing of electrons between two non-metals.

Example: Hydrogen chloride (HCl) formation involves hydrogen and chlorine sharing one electron pair.

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Metallic Bonding and Compound Structures

Metallic bonding involves positive metal ions surrounded by a sea of delocalized electrons. This structure gives metals their characteristic properties, such as conductivity and malleability.

Compounds can have different structures:

1. Giant Ionic Lattice: Found in ionic compounds, characterized by high melting/boiling points and conductivity when molten or dissolved.

2. Simple Covalent Compounds: Characterized by low melting/boiling points and poor electrical conductivity.

3. Giant Covalent Compounds: Include substances like diamond, graphite, and silicon dioxide, characterized by high melting/boiling points and varying electrical conductivity.

Example: Diamond is a giant covalent structure where each carbon atom forms four bonds, resulting in its extreme hardness.

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This comprehensive summary covers the key topics in AQA GCSE Chemistry Paper 1, providing students with essential information for exam preparation and revision.

Elements, Compounds, and Mixtures

The periodic table is a fundamental tool in chemistry, displaying all known elements. Each element consists of a single type of atom, while compounds are formed when two or more elements chemically bond together.

Definition: An element is a single type of atom found on the periodic table.

Example: Potassium (K) is an element with an atomic number of 19.

The structure of an atom includes a nucleus containing protons and neutrons, with electrons orbiting in shells. The atomic number represents the number of protons in an atom, while the mass number is the sum of protons and neutrons.

Vocabulary:

• Nucleus: The center of an atom containing protons and neutrons
• Electron: Negatively charged particles orbiting the nucleus
• Proton: Positively charged particles in the nucleus
• Neutron: Neutral particles in the nucleus

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