C2.1 Structure and Bonding

HideShow resource information

C2.1.1 Forming Ions

Chemical bonding involves either transferring or sharing electrons in the highest occupied energy levels of atoms in order to achieve the electronic structure of a noble gas. 

Noble gas structure: ions have the stable electronic structure of a noble gas from group 0, so have 8 electrons in their outer shell (except for helium which has 2) 

An ion forms when an atom transfers (either loses or gains) one or more electrons 

Positive ions: Metal and hydrogen atoms lose electrons to form positively charged ions. For example, sodium (2,8,1) loses its outer electron to form a sodium ion Na+ (2,8)

Negative ions: Non-metal atoms gain electrons to form negative ions. For example, a chlorine atom (2,8,7) gains one outer electron to form a chloride ion Cl- (2,8,8)

Patterns in the Periodic Table: The number of charges on a positive ion is the same as the group number of the element, and the number of charges on a negative ion is 8 minus the group number of the element

Group 1 = 1, Group 2 = 2+, Group 3 = 3+, Group 5 = 3-, Group 6 = 2-, Group 7 = -

1 of 5

C2.1.1 Ionic Compounds

Ionic compounds contain positive and negative ions, formed when atoms transfer electrons. Group 1 elements react with group 7 elements to produce ionic compunds.

Group 1 elements (alkali metals)

  • Metals
  • React with non-metals to form ionic compounds
  • Produce ions with a 1+ charge
  • e.g. lithium, sodium, potassium

Group 7 elements (halogens)

  • Non-metals
  • React with metal elements to form ionic compounds
  • Produce ions with a 1- charge
  • e.g. chlorine, bromine, iodine

Forming ionic compounds: e.g. sodium reacts with chlorine to form sodium chloride. The electron from the highest occupied energy level of Na is transferred to the highest occupied energy level of Cl, forming Na+ and Cl-

2 of 5

C2.1.1 Giant Ionic Structures

An ionic compound is a giant structure of ions:

  • Ions held in a regular arrangement: lattice
  • Ionic bonds
    • Strong electrostatic forces of attraction between oppositely charged ions
    • Act in all directions of the lattice and hold structure together

(http://www.bbc.co.uk/staticarchive/79adeab969839ce1f6e868e80d6cccf378fd0820.gif)

3 of 5

C2.1.1 Covalent Bonds

Covalent bonds form when atoms share electrons:

  • Forms between two non-metal atoms
  • Bonds between atoms are strong
  • Shared electrons form full outer shells in both atoms
  • Simple molecule e.g. H2, Cl2, O2, HCl, H2O, NH3 and CH4

(http://www.bbc.co.uk/staticarchive/bdd7c0044c8cb249325cabd9eb190b204dcad6c6.gif)
Shared electron from one atom is a dot and the other electron is shown as a cross

4 of 5

C2.1.1 Covalent Bonds in Macromolecules

Macromolecules have giant covalent structures and can be elements (like diamond) or compounds (like silica/silicon dioxide). Covalent bonds are usually represented by straight lines.

Diamond

  • Single molecule containing carbon atoms
  • Each carbon atom is covalently bonded to four other carbon atoms
  • Has a giant covalent structure

Silica

  • Each silicon atom is covalently bonded to four oxygen atoms
  • Each oxygen atom is covalently bonded to two silicon atoms
5 of 5

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Structure and bonding resources »