Chapter 5 – Atoms & Bonding

1. Chapter 5 – Atoms & Bonding

2. Valence Electrons & Bonding • Valence Electrons – the electrons the farthest away from the nucleus • The number of valence electrons in an atom of an element determines many properties of that element, including the ways in which the atom can bond with other atoms

3. Valence Electrons & Bonding • Electron Dot Diagram – includes the symbol for the element surrounded by dots…the dots show the valence electrons

4. Valence Electrons & Bonding • Atoms are more stable (less likely to react) when they have 8 valence electrons • Atoms can gain or lose electrons in order to have 8 valence electrons • Chemical Bond – the force of attraction that holds two atoms together

5. Chapter 5 – Atoms & Bonding • Section 3 - Covalent Bonds Standards • 3.b – Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements. • 7.c – Students know substances can be classified by their properties, including their melting temperature, density, hardness and thermal and electrical conductivity

6. Electron Sharing • Covalent Bond – a chemical bond formed when two atoms share electrons

7. How many Bonds? • Use electron dot diagrams to set up an atom to have 8 valence electrons • Electrons can be shared in order to fulfill the octet rule (8 valence electrons)

8. How many Bonds? • Double Bond – two pairs of electrons being shared between two atoms • Triple Bond – three pairs of electrons being shared between two atoms

9. Chapter 5 – Atoms & Bonding • Section 2 – Ionic Bonds Standards • 3.b – Students know that compounds are formed by combining two or more different elements and that compounds have properties that are different from their constituent elements. • 3.c – Students know that atoms and molecules form solids by building up repeating patterns, such as the crystal structure of NaCl or long-chain polymers

10. 10 electrons 8 valence e- Ions • Ion – an atom or group of atoms that has become electrically charged • When an atom loses an electron it has a positive charge • When an atom gains an electron it has a negative charge

11. Ions • Polyatomic Ion – ions that are made of more than one atom • Poly means ‘many’ • So polyatomic means ‘many atoms’

12. Ions • Ionic Bond – the attraction between two oppositely charged ions • Ionic bonds form as a result of the attraction between positive and negative ions • Ionic Compound – compound that consists of positive and negative ions

13. Chemical Formula & Names • Chemical F ormula – combination of symbols that shows the ratio of elements in a compound • Ex. MgCl2 or NaCl or K2S • When ionic compounds form, the ions come together in a way that balances out the charges on the ions • Subscript – tells you the ratio of elements in the compound • Ex. MgCl2 - 1 Magnesium ion and 2 Chlorine ions

14. Naming Ionic Compounds • The name of the positive ion goes first • Then the name of the negative ion • If the negative ion is an element, add the ending –ide • If the negative ion is polyatomic, leave the name the same Mg2+ + O2- MgO Magnesium Oxide Na+ + CO32-  Na2CO3Sodium Carbonate

15. Properties of Ionic Compounds • The characteristic properties of ionic compounds are: • Crystal Shape– orderly 3-D shape • High Melting Point– ionic bonds are strong • Electrical Conductivity– when dissolved in water, ionic compounds conduct electricity

16. Practice with Ionic Bonds • Examples: • Na + Cl  NaCl • Na+ + Cl– NaCl • Mg + Cl  MgCl • Mg2+ + Cl–  MgCl2 • Ca + O  CaO • Ca2+ + O2–  CaO • Al + O  AlO • Al3+ + O2–  Al2O3