Ions Noadswood Science, 2016

Ions Monday, April 16, 2018 To understand how atoms can become ions

Precise Learning There are three types of strong chemical bonds: ionic, covalent and metallic. For ionic bonding the particles are oppositely charged ions. For covalent bonding the particles are atoms which share pairs of electrons. For metallic bonding the particles are atoms which share delocalised electrons. Ionic bonding occurs in compounds formed from metals combined with non-metals. Covalent bonding occurs in most non-metallic elements and in compounds of non-metals. Metallic bonding occurs in metallic elements and alloys. Students should be able to explain chemical bonding in terms of electrostatic forces and the transfer or sharing of electrons. Elements that react to form positive ions are metals. Elements that do not form positive ions are non-metals.

Balloons How can you make a balloon gain a charge?

- - - - Balloons - - - - - - - - - - - - - - - + - - - + - + + + + - + + - - + + + - - + attraction + - - + - + + If the balloon is rubbed on your hair it picks up extra electrons – this makes it negatively charged Placing the balloon near a neutral object (i.e. the wall) the charges in the object move and cause the balloon to stick (opposite charges attract)… + - - - - - The balloon picks up –ve charges when rubbed on your head These –ve charges attract the +ve charges in the wall, and the balloon sticks…

Charge What charge do atoms usually have – why is this? Neutral atoms have no overall charge – this is because the charge of the electrons is the same as that of the protons, just opposite A neutral atom has no charge as the number of protons equals the number of electrons However, sometimes the charges can vary, in which case the atom is no longer regarded as neutral…

Atoms To Ions Atoms can gain a full outer shell (becoming stable) by either gaining or losing electrons when they react with other atoms When this reaction occurs atoms become ions Ions are electrically charged particles, formed when atoms lose or gain electrons – they have a charge because they contain an unequal number of electrons and protons…

Ions Atoms which lose electrons have more protons than electrons, and so have a positive charge – they are known as positive ions or cations Atoms which gain electrons have more electrons than protons, and so have a negative charge – they are known as negative ions or anions

Ions Metal atoms lose electrons and become positively charged ions (cations)

Electron arrangement [2.8]+ Metal Ions - Sodium Sodium atom: - 11 protons (charge = +11) 11 electrons (charge = -11) Total charge = 0 Sodium ion: - 11 protons (charge = +11) 10 electrons (charge = -10) Total charge = +1 + Na one electron is lost Na Electron arrangement 2.8.1 Electron arrangement [2.8]+

Electron arrangement [2.8]2+ Metal Ions - Magnesium Magnesium atom: - 12 protons (charge = +12) 12 electrons (charge = -12) Total charge = 0 Magnesium ion: - 12 protons (charge = +12) 10 electrons (charge = -10) Total charge = +2 Mg 2+ Mg two electrons are lost Electron arrangement 2.8.2 Electron arrangement [2.8]2+

Ions Non-metal atoms gain electrons and become negatively charged ions (anions) The name of an anion is slightly different to that of the atom, ending in ‘–ide’

Non-Metal Ions - Fluoride Fluorine atom: - 9 protons (charge = +9) 9 electrons (charge = -9) Total charge = 0 Fluoride ion: - 9 protons (charge = +9) 10 electrons (charge = -10) Total charge = -1 - F F one electron is gained Electron arrangement 2.7 Electron arrangement [2.8]-

Non-Metal Ions - Sulfide Sulfur atom: - 16 protons (charge = +16) 16 electrons (charge = -16) Total charge = 0 Sulfide ion: - 16 protons (charge = +16) 18 electrons (charge = -18) Total charge = -2 2- S S two electrons are gained Electron arrangement 2.8.6 Electron arrangement [2.8.8]2-

Building An Ion

Charges There is a quick way to work out what the charge on an ion should be… The number of charges on an ion formed by a metal is equal to the group number of the metal The number of charges on an ion formed by a non-metal is equal to the group number minus eight (hydrogen forms H+ ions)

Charges I II III IV V VI VII VIII Na Mg Al C N O Cl He 1+ 2+ 3+ * 3- Element example Na Mg Al C N O Cl He Charge 1+ 2+ 3+ * 3- 2- 1- ** Ion symbol Na+ Mg2+ Al3+ N3- O2- Cl- *Carbon and silicon (group IV) usually form covalent bonds (sharing electrons) **Elements within group VIII do not react with other elements to form ions

Practice Questions What are ions? What type of ions do metals form? What type of ions do non-metals form? What charge do the ions of Group 2 elements have?

Answers Charged particles formed when electrons are lost or gained by an atom or molecule Metals form positive ions Non-metals form negative ions +2