Chemistry

Elements- 1 type of atom Compound- 2+ elements chemically combined. Mixture- 2+ elements &/or compounds just mixed together; separated easilly. Atom- smallest part of matter. Molecule- 2+ atoms bonded together.

Nucleus- contains the protons and neutrons and nearly all the mass of the atom. Protons-mass of 1 has a single +ve charge. Neutron- mass of 1 no charge. Atomic mass- number of protons in the nucleus of the atom; different atoms have different atomic numbers. Mass number- number of protons + neutrons n the nucleus. Electrons- single -ve charge, which occupy shells around the nucleus. the number of electrons in a neutral atom is equal to the number of protons(atomic number). Isotopes-atoms of the same element having different mass numbers ie different numbers of neutrons.

The electrons in atoms are arranged in shells or energy levels like in this carbon atom:atomic number 6.

As you move outwards from the nucleus, the shells can hold more electrons The max number of electrons in each shell are: First shell- 2. Second shell- 8 .Third shell- 8 (up to element 20). Forth shell onwards- can contain up to 18 electrons.

The outer electrons of an atom are the ones that take part in chemical reactions therefore considering bonding we often only show the outer shell.

Bonding occurs between metals and non-metals like sodium chloride. The reaction can be represented as follows, showing the electron arrangement shown and the full form shown below:

Electrons are transfered from a metal to a non-metal forming two oppositely charged ions. Metals lose all outer shell electrons to the non-metal and become +ve charged ions, Non-metals gain electrons so become -ve charged ions.Both have the electronic structure of a Nobel gas. The ionic bond is the electrical attraction between these two ions.

Ions do not work on a 2D basis: they can attract oppositely charged ions in all directions, thus making a huge ionic lattice. In NaCl each cation is surrounded by 6 anions and vice verse. However, depending on the size of the ions, more or less can surround it.In all ionic solids, the ions are packed in a regular pattern, and held together by strong ionic bonds- this means that all ionic solids are crystalline. PropertyReason High melting and boiling pointsThe electrostatic forces between ions are very strong and alot of energy is required to break up the lattice. Very poor electrical conductivity as a solid. But very good when molten or dissolved. As a solid the conductivity is very poor because the electrons are all in a fixed position and cannot transfer charge.
However, when molten or dissolved the electrons are free to move. When dissolved the lattice separates into its charged ions: mobile charge carriers. Soluble in polar solvents (e.g. water) The lattice is broken up by the polarity of the solvent, this leaves the ions suspended in the solvent.

This is the joining together of non-metal atoms to form molecules,by sharing electrons, so that each atom has a nobal gas structure.1 shared pair of electrons=1 covalent bondThe outer shells of hydrogen & oxygen overlap so that the electrons can be shared.

Structural Formula : is where you use symbols and linesto represent covalent bonds. Eg methane

2 shared pairs between the atoms = double bondEg oxygen.

There are 2 types of covalent structure: GIANT covalent (macromolecular) & SIMPLE molecular.

Giant covalent- these substances consist of a giant molecule containing millions of atoms, joined together by covalent bonds. There are 3 giant structures of carbon(Diamond, Grapite, Bucky Balls) , but only 2 needed to know :-

DIAMOND- A carbon atom forms covalent bonds to 4 others.Each outer atom then bonds to 3 more, and so on. *It is very hard- because each atom is held in place by 4 strong bonds, for the same reason it has a *very high melting point.It also does *NOT conduct electricity, because there are ions or free electrons to carry the charge.

GRAPHITE- this is made of flat sheets of carbon atoms, each carbon atom forms covalent bonds to 3 others. this gives rings of 6 atoms, that join to make flat sheets. The sheets of atoms lie on top of each other, held together by weak forces. *high melting point. *it is soft and slippery, because the sheets of atoms can slide over each other easily. *It is a good conductor of electricity, because each atom has 4 outer electrons, but it forms only 3 bonds, so the forth electron is free & can carry charge.

Simple molecular- These can be elements or compounds, gases, liquids or low melting point solids.Each molecule contains (how ever many) atoms, held together by a strong covalent bond. But the molecules are held together by weak Inter molecular forces- can exist between molecules. They are WEAK and easily overcome by heating, they are found in covalent liquids & solids. All simple molecular solids are held together in a regular pattern; so solids are Ctystalline.

Properties- 1. low melting points& boiling points, because they are held together by weak forces. 2. Insoluble in water. 3.Soluble in petrol and tetrachlormethane. 4. Dont conduct electricity, because the molecules are not charged.

Metals have there own type of bonding & structure.

In a metal the atoms are arranged in layers, making up a lattice. the atoms are so close together that their outer electrons can move from one atom to the next one, these outer electrons form a "sea" or "cloud" of free moving electrons ; since the atoms have lost their electrons they become +ve ions.

Metallic Bonding: is the attraction between the moving( DELOCALISED ) electrons and the +ve ions in the lattice.

They are good conductors of electricity, because the delocalized electrons carry the charge.

They are good conductors of heat, because the free electrons can take in the heat energy, which makes them move faster. They pass some of it to their neighbours, during collisions. In this way the heat energy gets transferred all through the lattice.

They are malleable-can be hammered into different shapes, and ductile-can be drawn into wires, because the layers can slid over each other.

They have high melting points( except Group 1 metals which are the exception to the rule E.g mercury), because it takes a lot of energy to break up the lattice.