PRESENTED BY:PRESENTED BY:

S M OBAIDUL ARFIN.S M OBAIDUL ARFIN.

INSTRUCTOR: INSTRUCTOR: Ms. AFSHEEN KHALIL.Ms. AFSHEEN KHALIL.

PRESENTATION DATE:PRESENTATION DATE:

30 SEPTEMBER, 2006.30 SEPTEMBER, 2006.

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

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, H2O, tells us the number and type of each atom in the compound, so water molecules contain 2 hydrogen atoms combined with 1 oxygen atom.

COMPOUNDS Microscopic view

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

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.

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

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.

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.