Chemical Bonding

1. Chemical Bonding Valence Shells, Ionic Compounds, Molecular Compounds, Chemicals in Your Life

2. Chemical Families and Trends • The way in which elements come together to form compounds is based on their electron configurations • Bohr-Rutherford Model will provide us with a great model to work with

3. Parts of an Atom • Protons – are positively charged and have mass • Neutrons – are neutral in terms of charge an have mass. • Electrons – are negative and have relatively no mass

4. Chemical Families • Noble Gases – unreactive • Modern light bulbs are filled with argon so the tungsten filament will not react with oxygen and burn out • Eight electrons in the outer shell is called a stable octet • Halogens – one electron short of stability • Want to gain an electron to make a stable octet and will react with everything to try to achieve this

5. Chemical Families • Alkali Metals – one electron beyond stability • Wants to get rid of extra electron to reach stability • The most reactive alkali metal atoms are the largest • Sodium wants to shed one electron • What is it’s electron configuration like now?

6. Chemical Families • Alkaline Earth Metals – two electrons beyond stability • Will react vigorously but not as vigorous as the alkali metals (group 1) • Most reactive are the largest ones • Two fluorine atoms would be needed to react with one magnesium • Two electrons need to be discarded

7. Ionic Compounds • Stable Octets – NaF • Sodium can obtain a stable octet by releasing one of it’s electrons and fluorine can do the same by gaining an electron • Both will lose original properties though • Fluorine will have a negative charge • Sodium will have a positive charge • Alkaline Earth Metals? • Need to get rid of two electrons, how will that change the number of fluorine atoms that it will bind to?

8. Ionic Compounds • Ion – when an atom gains or loses an electron • Think about sodium…what if it were to lose one electron? • Think about fluorine…what if it were to gain one electron? • This has everything to do with how ionic bonding occurs • The positive ions are attracted to the negative ions and this creates an ionic bond • Electrons in outer shell are called valence electrons and this number is the same for all elements in a group • Lithium and oxygen example • Magnesium and oxygen example

9. Ionic Compounds • One common way to identify ionic compounds is that they are formed between metals and non-metals • Why would this hold true? • Ions in an ionic compound will fit together in a regular repeating pattern known as a crystal lattice • Not electrical conductors but when dissolved the ions come loose and they are excellent conductors

10. Molecular Compounds • Uncharged atoms come together to form compounds • Ionic compounds are formed when electrons are swapped (exchanged) however molecular compounds are based on the idea of sharing electrons • TWO NON METALS • This electron sharing is known as a covalent bond

11. Molecular & Ionic Compounds • What is the difference? • Covalent Bonds • Bonding between atoms is strong however the attraction between molecules is weak • Low attraction between molecules means low melting and boiling points • TWO NON METALS

12. Molecular & Ionic Compounds • Ionic Bonds • Strong attraction between molecules are it behaves like one large structure • METAL + NON METAL

13. Physical Properties • Colour and lustre – the light a substance reflects and its shininess. • Conductivity – ability of a substance to conduct heat to electricity. • Hardness – ability to hold its shape or be scratched. • Texture – how it feels or looks • Solubility – ability of substance to dissolve in water.

14. Chemical Properties • Reaction with acid – when substances react with acid often a gas is formed demonstrating a chemical change. • Reaction with water – same as above.