S2 Chemistry Covalent Bonding

Word Equations Learning Intention We are learning about covalent bonding

Success Criteria I can describe a covalent bond in terms of atoms sharing electrons I can explain how a covalent bond holds two atoms together. I can explain what is meant by a discrete molecule I can explain what is meant by a covalent network substance I can state that covalent bonds within a molecule are strong and that the forces of attraction between molecules are weak

The Covalent Bond The covalent bond is a shared pair of electrons between non metal atoms. H2 gas - + - +

The Covalent Bond The two atom are held together by the electrostatic attraction of the protons to the shared pair of electrons.

The Covalent Bond A molecule is 2 or more atoms joined by covalent bonds

The Covalent Bond The atoms share electrons so that they achieve the stable arrangement of the noble gasses.

The Covalent Bond The first electron energy level can only hold 2 electrons then it is full. Hydrogen achieves this stable arrangement by sharing an electron with another atom

The Covalent Bond When 2 fluorine atoms come close enough they overlap their electron clouds to share a pair of electrons x x o o x x o x F o F o x x o o

The Covalent Bond When 2 fluorine atoms come close enough they overlap their electron clouds to share a pair of electrons x x o o x x F F o o x o x x o o F F

The Covalent Bond Each atom would now appear to have the same electron arrangement as the noble gas neon. We can write the fluorine molecule as F-F or F2

The Covalent Bond Oxygen x x o x o o x o o x x o

The Covalent Bond Oxygen x o o x o x x x o o x o

The Covalent Bond Oxygen x o o x o x x o x o x o The oxygen molecule has two shared pairs of electrons It can be written as O O of O2

Conduction Covalent compounds never conduct electricity. Demo

Molecular Models Black = carbon White = hydrogen Red = oxygen Green = fluorine/chlorine/iodine Blue = nitrogen

Molecular Models It is very difficult to draw molecular models so chemists use a short version.

Molecular Models Use the molecular models to make up a model of – Fluorine Oxygen nitrogen

Molecules Molecules are described as discrete.

Molecules Molecules are described as discrete. This means that each molecule is separate from the next.

Molecules Molecules are described as discrete. This means that each molecule is separate from the next. Between the molecule there is very little holding them together

Molecules Molecules are described as discrete. This means that each molecule is separate from the next. Between the molecule there is very little holding them together Within the molecules they are held together by strong covalent bonds.

Molecular Explanations H O H O Strong covalent bond Within molecules H H Weak attraction between molecules

Electron Clouds The electrons in an atom are not actually arranged in the structured form shown in the target diagram.

Electron Clouds The electrons in an atom are not actually arranged in the structured form shown in the target diagram. x x x x x x x F x x

Electron Clouds The first level is spherical in shape while the second and third are tetrahedral. x x x x x x x F x x

Electron Clouds The first level is spherical in shape while the second and third are tetrahedral. x x x x x x x F x x

Electron Clouds The electrons fill each of the ‘petals’ singly at first and then they pair up. x x x x x x x x x F x x x x x x x

Electron Clouds The electrons fill each of the ‘petals’ singly at first and then they pair up. Single electrons x x x x x x x x x F x x x x x x x

Electron Clouds The tetrahedral shape of the clouds give an indication of the shape of the molecules.

Eg methane

Covalent Network Structures A covalent network structure is a vast 3-dimensional arrangement of atoms strongly bonded together by covalent bonds.

Covalent Network Structures Unlike molecules which have a definite formula, there is no fixed number of atoms in a covalent network.

Covalent Network Structures Each line in the diagram represents a covalent bond – a shared pair of electrons. In this way each carbon atom achieves the stable octet of electrons. The diamond structure can be described as a lattice because of its regular repeating pattern.

Covalent Network Structures There are only carbon atoms in diamond so the formula is just C. The formula for silicon dioxide, SiO2 indicates that the proportion of silicon atoms to oxygen atoms is 1:2

Covalent Network Properties Properties of silica Result appearance solubility melting conduction hardness

Covalent Network Properties Properties of silica Result appearance transparent solid solubility Not soluble in water melting 1713°C conduction no hardness Very hard

Covalent Network Properties Compared to molecular substances, covalent networks are very hard and have a very high melting point. Compared to ionic substances, covalent networks are not soluble in water and do not conduct when liquid (no charged particles).

Covalent Network Properties Covalent network substances are very hard solids because the strong covalent bonds extend throughout the structure To melt these substances the strong covalent bonds must be broken and this takes a considerable amount of energy.

Bonding Learning Intention We are learning about the 4 different types of bonding

Bonding Success Criteria I can describe the 4 types of bonding I can describe the properties of the different types of compounds I can give examples