1.2 Ions Year 9 Science 2012

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

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

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

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

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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

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

7 electrons in the outer shell Full outershell = 8 electrons

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

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

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-)

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

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

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

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

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

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

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”

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

Moving ions can conduct an electric current

Student Workbook – 1.5 Due ………………………………