Compounds are substances formed by chemically combining two or more elements. A compound consists of atoms of different elements bound together that have properties distinct from its constituent elements. There are two main categories of compounds: ionic compounds which contain positive and negative ions and exist as solids like NaCl, and covalent compounds which exist as neutral molecules like water and have lower melting/boiling points.

1. COMPOUNDS

2. PRESENTED BY: S M OBAIDUL ARFIN. INSTRUCTOR: Ms. AFSHEEN KHALIL. PRESENTATION DATE: 30 SEPTEMBER, 2006.

3. All substances have mass and therefore must be composed of atoms. These atoms and how they assemble themselves in the substance determines their chemical and physical properties. Substances can be classified according to how these atoms are assembled and is known as “Classification of Matter”. All matter falls into one of three categories: elements, compounds or mixtures.

5. COMPOUNDS A compound is a substance that is formed by chemically combining two or more elements. Water is formed when the elements hydrogen and oxygen combine. Its chemical formula , H 2 O, tells us the number and type of each atom in the compound, so water molecules contain 2 hydrogen atoms combined with 1 oxygen atom.

6. COMPOUNDS Microscopic view of the molecules of the compound water (gas phase). Oxygen atoms are red and hydrogen atoms are white.

7. COMPOUNDS Note that a compound: -consists of atoms of two or more different elements bound together , -can be broken down into a simpler type of matter (elements) by chemical means (but not by physical means), -has properties that are different from its component elements, -always contains the same ratio of its component atoms.

8. COMPOUNDS Names of some compounds: - Carbon dioxide, - Ethanol, - Glucose, - Chlorophyll.

9. COMPOUNDS Elements combine to form chemical compounds that are often divided into two categories. Metals often react with nonmetals to form ionic compounds . Nonmetals combine with each other to form covalent compounds , which exist as neutral molecules.

10. COMPOUNDS Ionic Compounds Contain positive and negative ions (Na+Cl-). Solids such as table salt (NaCl). High melting and boiling points. Strong force of attraction between particles. Separate into charged particles in water to give a solution that conducts electricity. Covalent Compounds Exist as neutral molecules (C6H12O2). Solids, liquids, or gases (C6H12O6(s), H2O(l), CO2(g)). Lower melting and boiling points (i.e., often exist as a liquid or gas at room temperature). Relatively weak force of attraction between molecules. Remain as same molecule in water and will not conduct electricity.

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