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C1 Fundamental Ideas

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Atomic Structure
The Periodic Table
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Keywords

Compound

Substance that contains at least two different elements, chemically combined


Mixture

Made up of many substances that can be easily separated

Element

A substance that cannot be broken down chemically (and is made up of all the same type of atom)


Ionic Compounds

Compounds formed from metals and non-metals consist of ions.


Covalent Compounds

Compounds formed from non-metals consist of molecules.

Atomic Structure

The atomic number is the number of protons.

The number of electrons = number of protons.

The number of neutrons = mass number – atomic number


Protons and neutrons have a relative mass of 1, whilst electrons have a relative mass of almost zero.


Protons have a charge of +1, electrons -1, and neutrons are neutral.

A carbon atom with 6 protons, 6 neutrons and 6 electrons

Chemical Symbols

Each element is represented by a chemical symbol. This consists of one or two different letters.


For example, C represents a carbon atom, and Na represents a sodium atom.


The first letter is always witten in UPPERCASE, but the subsequent letters is lowercase.


Conservation of Mass

No atoms are ever lost or made during a chemical reaction - but they can be rearranged. This means that the mass is always conserved.


This means that the total mass of products is equal to the total mass of the reactants.


Electron Configuration

Atoms fill to a maximum of 2 electrons in the first shell, 8 in the second and 8 in the third.


Each shell is filled before starting the next shell.

A diagram showing the electron arrangement of potassium

Balancing Equations

Higher

The same number of atoms of each element are needed on each side of an equation:

How to balance the reaction between sodium and chlorine

Covalent Bonding

These are compounds formed from only non-metals. These bonds form because the atoms share pairs of electrons to gain a full outershell. A covalent bond consists of two electrons being shared, usually one electron from each atom in the bond.


A dot and cross diagram showing the covalent bonding between carbon and hydrogen in methane

Ionic Bonding

These are compounds formed from metals and non-metals, and consist of ions.

Ions are charged particles that form when atoms (or molecules) lose or gain electrons.

Metal atoms lose electrons to form positively charged ions, and transfer their electrons to non-metal atoms which form negatively charged ions.


The ionic bond is the force of attraction between the oppositely charged ions.


A dot and cross diagram showing the bonding between sodium and chloride ions

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Atomic Structure
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Periodic Table

The Periodic Table is arranged in such a way that elements with the same properties can be found together in 'groups'.


Elements in the same group have the same number of electrons in their outshell (these are known as valance electrons).


Elements in the same period have the same number of electron shells.

The Periodic Table of elements

Group 1 (Alkali Metals)

React with water to form an alkaline solution:

Lithium + water —> lithium hydroxide + hydrogen

React vigorously when heated with chlorine gas:

Sodium + chlorine —> sodium chloride


Reactivity increases down the group – the outer negative electron is further from the positive nucleus so more easily lost.


Lower melting and boiling points down the group.


Group 0 (Noble Gas)

Full outer shells so are inert.


Boiling point increases down the group as atoms have more electrons so stronger intermolecular forces form between molecules.


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Atomic Structure
The Periodic Table
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Page last updated: 14/04/2017