Chemistry- Topic 2

• Ions are made when electrons are?

  transferred
• What are ions?

  charged particles
• Why do atoms lose or gain electrons

  To get a full outer shell so that they are 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 charge on an ion is the same as


  the number of electrons gained or lost
• what groups are most likely to form ions?

  1,2,6,7
• which elements most readily form ions?

  groups 1,2,6 and 7
• Group 1 and 2 elements

  lose electrons to form positive ions (cations)
• group 6 and 7 elements

  gain electrons to form negative ions (anions)
• Elements in the same group all have the same number of outer electrons so ...

  they 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
• equation: sodium atom loses an electron

  Na --> Na+ + e-
• equation: magnesium atom loses 2 electrons

  Mg --> Mg2+ + 2e-
• equation: chlorine atom gains 1 electron

  Cl + e- → Cl-
• equation: oxygen atom gains 2 electrons

  O + 2e- --> O2-
• If the atom is becoming a positive ion and losing electrons then you place the electron on the

  right
• if atom is gaining electrons you place the electron on the

  left to show that its combining with the atom
• explain why simple ions often have noble gas electronic structures. (2)

  Noble gas electronic structures have a full shell of outer electrons, which is a very stable structure
• ionic bond

  the attraction between oppositely charged ions
• Ionic bonding

  The electrostatic attraction between positive and negative ions
• ionic bonding- transfer of electrons

  When a metal and non-metal react together, the METAL atom LOSES electrons to form a POSITIVELY CHARGED ION and the NON-METALS GAIN 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.
• Describe, in terms of electron transfer, how sodium (Na) and chlorine (Cl) react to form sodium chloride (NaCl). (3)

  Each sodium atom loses an electron to form an Na+ ion. Each chlorine atom gains an electron to form Cl- ion. The oppositely charged ions are attracted to each other by electrostatic attraction.
• ionic compound properties

  -HIGH MELTING/BOILING POINTS (due to the many strong bonds between the ions)

  -When solid it CANT CONDUCT ELECTRICITY (ions are held in place . when ionic compounds melt, the ions are free to move and they'll carry electrical current)

  -Dissolve easily in water ( The ions separate and are all free to move in the solution, so they'll carry electric current.
• What is the structure of ionic compounds?

  Giant ionic lattice ( The ions form a closely packed regular lattice arrangement with strong electrostatic forces of attraction between oppositely charged ions, in all directions)
• the structure of an ionic compounds

  Giant ionic lattice
• the structure of the ionic compound of chloride ion and caesium ion. Predict , with reasoning, whether the compound has a high or a low melting points

  It has a high melting point because a lot of energy is needed to break the ionic bonds.
• Explain why ionic compounds have a giant structure

  Ionic compounds have giant structures because the ions keep their charge and attract up to 6 other ions - forming a giant lattice
• explain why ionic compound can conduct electricity when molten

  When melted the ions are free to move, so they can carry an electric current
• Covalent bonds are formed between

  two nonmetals
• covalent bonds are made when ..

  non metal atoms bond together and share pairs of electrons
• why are non metals strong?

  The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces
• Limitations of dot and cross diagrams (bonding in ionic compounds)

  1) They're useful for showing which atoms the electrons in an ion/covalent bond come from

  but they don't show the structure of the compound, the size of the ions/atoms or how they are arranged.
• Limitations of displayed formula

  1) its a great way of showing how atoms are connected in large molecules.

  but don't show the 3D structure of the molecule, or which atoms the electrons in the covalent bond have come from
• Limitations of 3D model

  The 3D model shows the covalent bonds and their arrangement.

  but they get confusing for large molecules and don't show where the electrons in the bond have come from
• Substances containing covalent bonds usually have simple molecular structures, State the properties of simple molecular substances


  1) The atoms within the molecules are held together by STRONG covalent bonds but WEAK intermolecular forces

  2) very LOW MELTING and BOILING points (as you only need to break the weak intermolecular forces and not the covalent bonds).

  3) most molecular substances are GASES or LIQUIDS at room temperature.

  4) Molecular compounds DON'T CONDUCT ELECTRICITY (they aren't charged so there are no free electrons)

  5) As molecules get bigger, the strength of the intermolecular forces increases, so more energy is needed to break them, and the bp and mp increase
• Explain why oxygen is a gas at room temperature? (1)

  The INTERMOLECULAR FORCES between molecules of oxygen are WEAK and don't need much energy to break