Why are atoms neutral despite having charged particles
There are lots of dot and cross diagrams i.e. Lewis diagrams of bonding situations
INTRODUCTION TO CHEMICAL BONDING
When different elements (different types of atom) react and combine to form a compound (new substance) chemical bonds must be formed to keep the atoms together. Once these atoms are joined together its usually difficult to separate them.
The atoms can join together by sharing electrons in what is known as a covalent bond.
Or, they can transfer or accept electrons to form positive and negative ions and form an ionic bond.
Metals form another kind of bond in sharing electrons called a metallic bond.
The types of are briefly explained below with links to even more detailed notes with lots of examples.
Part 1 begins by explaining why atoms bond together in the first place and then the concepts broadened out to explain the different types of bonding.
Some atoms are very reluctant to combine with other atoms and exist in the air around us as single atoms. These are the Noble Gases and have very stable electron arrangements e.g. 2, 2,8 and 2,8,8 because their outer shells are full. The first three are shown in the diagrams below and explains why Noble Gases are so reluctant to form compounds with other elements.
(atomic number) electron arrangement
All other atoms therefore, bond together to become electronically more stable, that is to become like Noble Gases in electron arrangement. Bonding produces new substances and usually involves only the 'outer shell' or 'valency' electrons and atoms can bond in two ways.
The phrase CHEMICAL BOND refers to the strong electrical force of attraction between the atoms or ions in the structure. The combining power of an atom is sometimes referred to as its valency and its value is linked to the number of outer electrons of the original uncombined atom (see examples later).
Each type of chemical bonding is VERY briefly described below, with links to more detailed notes.
(a) IONIC BONDING – an ionic bond is formed by one atom transferring electrons to another atom to form oppositely charged particles called ions which attract each other – the ionic bond. An ion is an atom or group of atoms carrying an overall positive or negative electric charge
The atom losing electrons forms a positive ion (cation) and is usually a metallic element.
The atom gaining electrons forms a negative ion (anion) and is usually a non–metallic element.
The ionic bond then consists of the attractive force between the positive and negative ions in the structure.
The ionic bonding forces act in all directions around a particular ion, it is not directional, as in the case of covalent bonding.
The sodium (metal) atom transfers an electron to the chlorine (non–metal) atom in forming the ionic compound sodium chloride
The bonds between the ions is very strong and they club together to form a giant ionic
lattice with a very high melting point because it takes a lot of energy to overcome the attractive forces between the ions - the ionic bonds.
When molten, or dissolved in water, ionic compounds will conduct electricity because the charged particles (ions) are free to move and carry the electric current.
For more detailed notes on this example and lots of other examples.
(b) COVALENT BONDING – a covalent bond is formed by two atoms sharing electrons so that the atoms combine to form molecules.
The bond is usually formed between two non–metallic elements in a molecule. The two positive nuclei (due to the positive protons in them) of both atoms are mutually attracted to the shared negative electrons between them forming the covalent bond. They share the electrons in a way that gives a stable Noble Gas electron arrangement like helium (2) or neon (2.8) etc.
This kind of bond or electronic linkage does act in a particular direction i.e. along the 'line' between the two nuclei of the atoms bonded together, this is why molecules have a particular shape.
Hydrogen and oxygen atoms share electrons to give covalent O–H bonds to form molecules of the covalent compound water
which has a 'bent' shape
More detailed revision notes on this example and other examples see.
(c) METALLIC BONDING isn't quite like ionic or covalent bonding, although the metal atoms form positive ions, no negative ion is formed from the same metal atoms, but the immobile positive metal ions/atoms in the lattice are attracted together by the free moving negative electrons between them. So, like ionic bonding, you do get attraction between positive and negative particles and this is the metallic bond.
(d) INTERMOLECULAR FORCES – INTERMOLECULAR BONDING
Between all particles, but with particular reference to covalently bonded molecules. there always exists some very weak electrical attractive forces known as intermolecular forces or intermolecular bonding.
These constantly acting attractive forces or intermolecular bonds are very much weaker than full covalent or ionic chemical bonds (approximately 1 /30 to 1 /20 th in comparative attractive force).
For example, although the oxygen and hydrogen atoms are very strongly bonded in water to make a VERY stable molecule, BUT this does NOT account for the existence of liquid water and ice!
It is the weak intermolecular forces that induces condensation below 100 o C and freezing–solidification to form ice crystals below 0 o C.
In the reverse process, when ice is warmed, the intermolecular forces are weakened and at 0 o C the intermolecular bonds are weakened enough to allow melting to take place.
Above 0 o C (evaporation), and particularly at 100 o C (boiling), the intermolecular forces are weak enough for 'intact water molecules' to escape from the surface of the liquid water.
It is VERY important to realise that the chemical hydrogen–oxygen covalent bonds (O–H) in water are NOT broken and the state changes.
solid <== freezing/melting ==> liquid <== condensing/boiling ==> gas.
are due to the weakening of the intermolecular forces/bonds with increase in temperature OR the strengthening of the intermolecular bonds/forces decrease in temperature.
(e) WHY DO SOME ATOM DO NOT READILY FORM CHEMICAL BONDS?
As explained at the start of Part 1, NOBLE GASES are very reluctant to share, gain or lose electrons to form a chemical bond ie they do NOT readily form a covalent or ionic bond with other atoms.
Noble gases are already electronically very stable because of their particular electron arrangement.
e.g. 2, 2.8 and 2.8.8 etc.
For most other elements the types of bonding and the resulting properties of the elements or compounds are described in detail in Parts 2 to 5. In some of the electronic diagrams ONLY the outer electrons are shown.
(f) Can we deduce the likely chemical bonding in a material from its physical and chemical properties.
The answer quite simply is YES, as long as you have studied parts 2 to 5 before attempting this question!
The table below describes the properties of. compounds. The data is not specific to a substance, just 'typical properties'Source: www.docbrown.info