Covalent Bonding 1 of 27 Boardworks Ltd 2016
Covalent Bonding 2 of 27 Boardworks Ltd 2016
Why do atoms form bonds? 3 of 40 Boardworks Ltd 2016
What is a covalent bond? 4 of 40 Boardworks Ltd 2016 Non-metal elements usually just need one or two electrons to fill their outer shells. incomplete outer shells The two non-metal atoms cannot form a bond by transferring electrons from one to another. Instead, they share electrons. Each atom now has a full, stable outer shell. The shared electrons join the atoms together. This is called a covalent bond.
How are covalent bonds drawn? 5 of 40 Boardworks Ltd 2016 How do we draw covalent bonds? dot and cross In a dot and cross diagram, the covalent bond is shown by a pair of shared electrons. structural formula In the structural formula, atoms are shown by their chemical formula, and the bond is shown by a solid line. ball and stick In a ball and stick model, the balls show the atoms and the sticks show the covalent bonds.
Dot and cross diagrams 6 of 40 Boardworks Ltd 2016 Only the outer shells of electrons are involved in bonding, so the inner shells do not always have to be included in dot and cross diagrams. simplify In fact, you don not even need to draw the circle for the outer shell. simplify
How are covalent bonds formed? 7 of 40 Boardworks Ltd 2016 When atoms share pairs of electrons, they form covalent bonds. covalent bond = shared electrons These bonds between atoms are strong. + + electrostatic attraction Covalent bonds are a result of electrostatic attraction between the positively-charged nuclei of the atoms and the negatively-charged shared electrons.
Comparing covalent and ionic bonding 8 of 40 Boardworks Ltd 2016
Covalent Bonding 9 of 27 Boardworks Ltd 2016
Which elements form covalent bonds? 10 of 40 Boardworks Ltd 2016 How do non-metal atoms form covalent bonds?
Covalent bonding in hydrogen 11 of 40 Boardworks Ltd 2016 Many non-metal elements, such as hydrogen, exist as simple diatomic molecules that contain covalent bonds. How is a covalent bond formed in hydrogen? H H H H Each hydrogen atom needs one more electron in its outer shell and so each atom shares its single unpaired electron. This shared pair of electrons forms a covalent bond and so creates a diatomic molecule of hydrogen.
Single, double and triple bonds 12 of 40 Boardworks Ltd 2016
13 of 40 Boardworks Ltd 2016 Diatomic molecules Oxygen is a diatomic molecule with a double covalent bond. Nitrogen is a diatomic molecule with a triple covalent bond. Element Molecule Dot and cross diagram Hydrogen (1) H 2 H H Chlorine (2.8.7) Oxygen (2.6) 2 O 2 O O Nitrogen (2.5) N 2 N N
Covalent bonds in compounds 14 of 40 Boardworks Ltd 2016 Covalent bonding can also occur between atoms of different non-metals to create molecules of covalent compounds. These covalent bonds can be single, double or triple. How is a covalent bond formed in hydrogen chloride (H, also represented as H )? H H Hydrogen and chlorine both need one more electron to fill their outer shells. By sharing one electron each, they both have a stable outer shell and a covalent bond is formed.
15 of 40 Boardworks Ltd 2016 Covalent bonding in water Compounds can contain more than one covalent bond. Oxygen (2.6) needs two more electrons, but hydrogen (1) only needs one more. How can hydrogen and oxygen be joined by covalent bonding? The oxygen atom shares one electron with one hydrogen atom, and a second electron with another hydrogen atom. H O H What is the name of the molecule that is formed? H 2 O (or H O H) is water.
Calculating the ratio of atoms 16 of 40 Boardworks Ltd 2016
17 of 40 Boardworks Ltd 2016 Drawing simple covalent molecules Molecular formula Dot and cross Structural formula Example NH 3 H N H I H Simple to draw Ball and stick Shows that electrons are shared Shows which atoms are connected Shows the 3D arrangement
Models of covalent molecules 18 of 40 Boardworks Ltd 2016 Two dimensional diagrams of covalent molecules can be converted into three dimensional models. H I H C H I H This is the structural formula of methane. Make a model to show the 3 dimensional structure. Start with a ball to represent the carbon atom. Attach 4 sticks to represent the bonds. Put a ball on the end of each stick to represent the hydrogen atoms.
19 of 40 Boardworks Ltd 2016 Covalent compounds Fill in the table below. Elements Molecule 2D 3D Hydrogen (1) Chlorine (2.8.7) Hydrogen (1) Oxygen (2.6) H Hydrogen chloride H 2 O Water H H O H Hydrogen (1) Nitrogen (2.5) Hydrogen (1) Carbon (2.8.4) NH 3 Ammonia CH 4 Methane H N H I H H I H C H I H
Covalent bonds true or false? 20 of 40 Boardworks Ltd 2016
Covalent Bonding 21 of 27 Boardworks Ltd 2016
Covalently bonded substances 22 of 40 Boardworks Ltd 2016 We have seen that simple molecules with a small number of atoms can contain covalent bonds. Some other covalently bonded substances include: polymers (e.g. plastics, rubber and DNA) giant covalent structures (e.g. sand, diamond and graphite)
What are polymers? 23 of 40 Boardworks Ltd 2016 Polymers are made when hundreds of simple covalent molecules join together to form a long chain. The molecules that join together to make a polymer are called monomers. The word polymer comes from the Greek words poly (meaning many ) and meros (meaning parts ).
What are giant covalent structures? 24 of 40 Boardworks Ltd 2016 Giant covalent structures, such as sand (SiO 2 ), diamond and graphite, are made from millions of atoms joined together by covalent bonds. O O O Si O The arrangement of atoms and bonds repeats itself in three dimensions to form a giant regular lattice.
Covalent Bonding 25 of 27 Boardworks Ltd 2016
Glossary 26 of 40 Boardworks Ltd 2016
Multiple-choice quiz 27 of 27 Boardworks Ltd 2016