C1- Chemistry- C1.1 - 1.5 (Fundamental Ideas)

• There are about 100 different types of atoms & therefore only about 100 elements
• Some substances are made up of one type of atom --> These are called substance elements
• Elements contain only one type of atom
• Compounds contain more than one 
• An atom has a tiny nucleus surrounded by electrons.

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Different Types of elements:

The Alkali Metals- Very reactive, not found naturally.

The Alkaline Earth Metals- Very reactive (Oxidation number of +2), not found free in nature.

The Transition Metals- Ductile and Maleable, conduct electricty and heat.

The Halogens- Compounds containing Halogens are 'salts'. All halogens have 7 electrons in their outer shell, (Oxidation number of -1) They exist at room temprature in all 3 states of matter.

• Solid- Iodine, Astatine
• Liquid- Bromine
• Gas- Fluorine, Chlorine 

The Noble Gases-  'Inert gases' (Oxidation number of 0) This prevents them from forming compounds easily. Full outter shell of electrons making them stable.

• The Nucleus contains protons and neutrons.
• Atoms are made of protons, neutrons and electrons.
• Protons and electrons have equal and opposite electric charges. 
  
• Atomic number =Number of Protons (=Number of Electrons) 
• Mass number = Number of Protons + Neutrons
• Atoms are arranged in the Periodic tbale in order of their atomic number

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Proton  +1

Neutron  0        (Have no electrical charge. They are neutral)

Electron -1

• The electrons in an atom are arranged in energy levels or shells.
• Atoms with the same number of electrons in their outermost shell belong in the same group of the periodic table
• The number of electrons in the outer most shell of an element's atom determines the way that element reacts.

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Electron Shell Diagrams

• The first shell can only hold 2 electrons
• Each shell after that can hold up to 8 electronsper shell.

Forming Ions

When a metal bonds with a non-metal, the metal atom gives one or more electron to the non-metal atom. Both atoms become charged particles called ions.

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• Metal atoms form positively charged ions (+)
• Non-metal atoms form negatively charged ions (-)

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Opposite charges attract each other. There are stron attractions between the possitive and negative ions in a compound of a metal and non-metal. These strong forces of attraction are the chemical bonds that form. They are called ionic bonds.

In compounds between metals and non-metals, the charges on the ions always cancel each other out. This means their compound has no overall charge. Eg- Lithium Fluoride = LiF

Forming Moleules

Non-metals bond in a different way. The outtermose shells overlap and they share electrons. This is called a Covalent Bond.

• No ions are formed
• They form molecules- Eg- hydrogen sulfide H2S and Methane CH4

Word Equations

Chemical equations show the products and the reactants. We can represent this using a word equation:

• Hydrogen + Oxygen -> Water

             ^Reactants = ^Products

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Symbol Equations

Symbol equations helps us see how much of each substance is reacting.

• CaCO3 -> CaO + CO2

This equation is balanced- there is the same number of each type of atom on both sides of the equation. This means that- The total mass of the products formed in a reaction is equal to the total mass of reactants.

• Word equations are only useful if everyone who reads them speaks the same language.
• Word equations do not tell us how much of each substance is involved in the reaction.
• Word equations can get very complicated when lots of chemicals are involved