grade8chapterrrrrrrrrrrr2-211211133705.pptx
- 1. Chapter 2: Structure of Matter Atoms, Molecules and Ions Chemistry Grade 8 Unit 2 Done by Ms. Sara Chehab
- 2. The Atom • Theatomis thebasicbuilding blockfor all matter in theuniverse. Forexample,air is madeupof atoms. Thecomputerismadeupofatoms. Ourhandsaremadeupof atoms. Everythingis madeupof atoms.
- 3. Atomsareextremelysmallandaremadeupofa fewevensmaller particles called subatomic particles:electrons, protons,andneutrons.
- 4. An atom is neutral (has no charge). The negative charge of the electrons is enough to neutralize the positive charge of the protons. An atom contains equal number of protons and electrons.
- 5. Each element has a unique atom. For example, the hydrogen atom is different than the oxygen atom. And the oxygen atom is different than the carbon atom.
- 6. The number of protons in an atom determines the identity of the element. This number is called the atomic number of the element and is denoted by the letter Z. See the following examples: Helium atom has 2 protons, so it has atomic number Z=2 Nitrogen atom has 7 protons, so its atomic number Z = 7 Sodium atom has 11 protons, so its atomic number Z = 11
- 7. The Molecule A molecule is a neutral group of atoms joined together by a chemical bond. Hydrogen molecule is made up of 2 hydrogen atoms bonded together. Water molecule H2O is made up of 2 Hydrogen atoms and one oxygen atom bonded together Carbon dioxide molecule is made up of one carbon atom and two oxygen atoms bonded together. Examples:
- 8. Diatomic Molecules: Diatomic molecules are moleculescomposed ofonlytwoatoms,of the sameor different chemical elements. Examples:
- 9. Molecular Elements: Molecular elements are molecules that have two or more atoms of the same elementbonded together. Examples:
- 10. Molecular Compounds: Molecular compounds are molecules made up of two or more different elements. Examples:
- 11. The Ion: The ion is anatomor groupof atomsthat carries a positive or negative charge as a result of having lost or gained oneor more electrons. Examples:
- 12. • A positively charged ion is called a “cation”. • A negatively charged ion is called an “anion”.
- 13. Cations are formed when atoms lose electrons. Examples:
- 14. Anions are formed when atoms gain electrons. Examples:
- 15. Let us discuss some examples: A magnesium atom has atomic number Z = 12. We know that in an atom the number of electrons is equal to that of protons. So, number of electrons = 12. If a Magnesium atom loses 2 electrons it will then have 10 electrons and 12 protons. The charge of magnesium ion is : +12-10 = +2
- 16. A chlorine atom has atomic number Z = 17. So the number of electrons = number of protons = 17. If a chlorine atom gains one electron, then the number of electrons becomes 18. So, the charge of a chloride ion = +17-18 = -1
- 17. Monoatomic & Polyatomic Ions: Note: Ions that contain only two atoms are called diatomic ions.