Chapter 5: Formations of Ions and Bonding

5.1-Formations of Ions

Ions are made when electrons are transferred

• Ions are charged particles-they can be single atoms or groups of atoms
• When atoms lose of gain electrons to form ions, all they’re trying to do is get a full outer shell like a noble gas
  • Atoms with full outer shell are very stable
• When metals form ions, they lose electrons from their outer shell to form positive ions
• When non-metals form ions, they gain electrons into their outer shell to form negative ions
• The number of electrons lost or gained is the same as the charge on the ion
  • E.g. If 2 electrons are lost the charge is 2+.
  • If 3 electrons are gained the charge is 3-

Groups 1&2 and 6&7 are the most likely to form ions

• The elements that most readily form ions are those in Group 1,2,6 and 7
• Group 1 and 2 elements are metals and they lose electrons to form positive ions(cations)
• Group 6 and 7 elements are non-metals and they gain electrons to form negative ions(anions)
• You don’t have to remember what ions most elements form
  • You just look at the periodic table
• Elements in the same group all have the same number of outer electrons
• So they have to lose or gain the same number to get a full outer shell
  • This means that they form ions with the same charges
• Group 1 elements form 1+ ions
• Group 2 elements form 2+ ions
• Group 6 elements form 2- ions
• Group 7 elements form 1- ions

Examples of formation:

• A sodium atom is in Group 1 so it loses 1 electron to form a sodium ion with the same electronic structure as a neon
  • Na-Na+ + e-
• A magnesium atom is in Group 2 so it loses 2 electrons to form a magnesium ion with the same electronic structure as neon
  • Mg-Mg2+ + 2e-
• A chlorine atom is in Group 7 so it gains 1 electron to form a chloride ion with the same electronic structure as argon
  • Cl + e- - cl-
• An oxygen atom is in Group 6 so it gains 2 electrons to form an oxide ion with the same electronic structure as neon
  • O + 2e- - O2-

5.2-Ionic Bonding

Ionic bonding-transfer of electrons

• When a metal and a non-metal react together, the metal atom loses electrons to form a positively charged ion and the non-metal gains these electrons to form a negatively charged ion
• These oppositely charged ions are strongly attracted to one another by electrostatic forces
  • This attraction is called an ionic bond

Dot and cross diagrams show how ionic compounds are formed

• Dot and cross diagrams show the arrangement of electrons in an atom or ion
• Each electron is represented by a dot or a cross
• So these diagrams can show which atom the electrons in an ion originally came from
  • Sodium chloride
  • The sodium atom gives up its outer electron, becoming an Na+ ion
  • The chlorine atom picks up the electron, becoming a Cl- ion
  • Magnesium chloride
  • The magnesium atom gives up its two outer electrons, becoming an Mg2+ ion
  • The two chlorine atoms picks up one electron each, becoming two Cl- ions
  • Sodium oxide
  • Two sodium atoms each give up their single outer electron, becoming two Na+ ions
  • The oxygen atom picks up the two electrons, becoming an 02- ion
• Dot and cross diagrams are useful for showing how ionic compounds are formed, but they don’t show the structure of the compounds, the size of the ions or how they’re arranged.

5.3-Ionic Compounds

Ionic compounds have a regular lattice structure

• Ionic compounds have a structure called a giant ionic lattice
• The ions form a closely packed regular lattice arrangement and there are very strong electrostatic forces of attraction between oppositely charged ions
  • In all directions in the lattice
• A single crystal of sodium chloride(table salt) is one giant ionic lattice
• The Na+ and Cl- ions are held together in a regular lattice
• The lattice can be represented in different ways:
  • A model could show the relative sizes of the ions as well as the regular pattern of an ionic crystal, but it only lets you see the outer layer of the compound
  • A model could show a ball and stick model
  • It would show the regular pattern of an ionic crystal and show how all the ions are arranged
  • It also suggest that the crystal extend beyond what’s shown in the diagram
  • The model isn’t to scale so the relative sizes of the ions may not be shown
  • Also in reality there aren’t gaps between the ions

Ionic compounds all have similar properties

• They all have high melting and boiling points due to the many strong bonds between the ions
  • It tales lots of energy to overcome this attraction
• When they’re solid, the ions are held in place, so the compounds can’t conduct electricity
• When ionic compounds melt, the ions are free to move and they’ll carry electric current
• Some ionic compounds also dissolve in water
  • The ions separate and are all free to move in the solution, so they’ll carry electric current

Look at charges to find the formula of an ionic compound

• You might have to work out the empirical formula of an ionic compound from a diagram of the compound
• If it’s a dot and cross diagram, count up how many atoms there are of each elements
  • Write this down to give you the empirical formula
• If you’re given a 3D diagram of the ionic lattice, use it to work out what ions are in the ionic compound
  • You’ll then have to balance the charges of the ions so that the overall charge on the compound in zero

5.4-Covalent Bonding

Covalent Bonds-sharing electrons

• When non-metal atoms bond together, they share pairs of electrons to make covalent bonds

• The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong

• Atoms only share electrons in their outer shells

  • Highest energy levels

• Each single covalent bond provides one extra shared electron for each atom

• Each atom involved generally makes enough covalent bonds to fill up its outer shell

  • Having a full outer shell gives them the electronic structure of a noble gas, which is very stable

• Covalent bonding happens in compounds of non-metals and in non-metal elements

  

There are different ways of drawing covalent bonds

• You can use dot and cross diagrams
• You can use 3D models
  • By using the molecular formula