1. 1.2 Ions
Year 9 Science
2012

2. Atoms and Ions
Since atoms are electrically neutral (no charge) they have the same number of protons (positive) and electrons (negative)
But, if an electrons is REMOVED or ADDED, the atom becomes charged and is now called an ION

3. Ions:
If an electron is removed, the neutral atom becomes a charged POSITIVELY CHARGED ION
A positively charged ion is called a CATION
If an electron is added, the neutral atom becomes a NEGATIVELY CHARGED ION
A negatively charged ions is called an ANION

4. Cations: Here one electron removed
Now, there is one more proton than the number of electrons
So, the ion is positively charged

5. Cations and Metals: Almost all cations come from metals
Metals only have a few electrons in their outer shells and these electrons are WEAKLY bound to the atom
Weakly held electron

7. Page 14 of Science9

8. The Hydrogen ion (H+)
Another important positive ion (cation) is the hydrogen ion (H+)
Hydrogen ions (H+) are formed when ever an acid is dissolved in water

9. Anions:
If a neutral atoms gains an electron a negative ion or ANION is formed
If the outermost shell of the atom is ALMOST FULL, the atom can gain an additional electron until the shell is full

10. 7 electrons in the outer shell
Full outershell = 8 electrons

11. Anions , mostly non-metals
All ions come from non-metals
All of these atoms can gain an electron to fill their outer shell

12. Ionic Compounds
When anions and cations come together, they form compounds made up of large crystal lattices
These compounds are also known as IONIC COMPOUNDS

14. Chemical Names and Formulas
To name ionic compounds you write the name of the cation followed by the name of the anion
Eg Calcium Oxide = Calcium cations (Ca2+ ) and Oxygen anions (O2-)
Copper (I) chloride = Copper (I) cations (Cu+) and chloride anions (Cl-)

15. Writing the chemical formula:
The chemical formula for an ionic compound MUST show an EQUAL number of positive and negative charges.
The total charge must be zero
Eg The sodium ion has a charge of +1 and the Chloride ion has a charge of -1
So the chemical formula is just NaCl, as you only need one (1) of each ion to fully balance the charges

16. For magnesium chloride:
Magnesium ion has a charge of +2
Chloride ion has a charge of -1
So, two chloride ions are needed to balance the charge of each magnesium ion
So the formula for magnesium chloride is MgCl2

17. Ionic Bonding:
Anions and cations are attracted to each other as they have opposite charges
They stick together they form an IONIC BOND

18. Properties of Ionic Bonds
Ionic bonds are very strong, so ionic compounds are usually:
Are hard
Are brittle
Have a high melting points

19. Why?
Ionic compounds are hard because it takes a lot of force to break the ionic bonds
They are brittle because the ionic bond holds the ions in fixed positions, to the lattice shatters rather than bends
Ionic compounds have high melting and boiling points because high temperatures are needed to break the strong ionic bonds

21. Ions in solution: Some ions are soluble or dissolve in water
Other ions are insoluble (do not dissolve) in water
How easily a substance dissolves is called its SOLUBILITY

23. Dissolving in Water – What happens?
When an ionic substance dissolves in water, the water particles SURROUND the cations and anions
This breaks the crystal lattice apart and stops the ions from sticking back together
The ions then spread evenly throughout the solution
The ions are said to be “in solution”

25. If the water is removed, by boiling or evaporation, the ions stick together once more

26. Moving ions can conduct an electric current

27. Student Workbook – 1.5
Due ………………………………