element: a pure substance which cannot be broken down further by ordinary chemical or physical processes

atom: the smallest particle of an element which retains the chemical properties of that element

Atoms are made of electrons, protons, and neutrons. All atoms of a particular element have a unique no. of protons.

compound: a pure substance composed of two or more elements in fixed proportions, e.g., water, rust, ammonia

States of matter

solid-fixed volume & shape

liquid-fixed volume & takes on shape of container

gas-takes on volume & shape of container

Why do substances assume the states that they do?

phase determined by:

1. temperature

2. pressure

3. forces between particles

Mixtures

1. homogeneous: properties uniform throughout mixture,

e.g., salt water, air, gasoline, brass

2. heterogeneous: properties not uniform throughout mixture,

e.g., soil, an egg, oil + water, milk

physical change: a change in form but not in chemical composition, e.g., breaking or melting ice

chemical change: a change in which the chemical composition of a substance changes, e.g., combustion of gasoline

(organization of matter diagram)

Units used in chemistry

quantity	SI unit	others
mass	kilogram, kg	gram, g
length	meter, m	centimeter, cm (10-2) nanometer, nm (10-9) angstrom, Å (10-10)
time	second, s	.
temperature	Kelvin, K	degrees Celsius, oC
volume	cubic meter, m3	liter, L milliliter, mL (1 cm3)
energy	joule, J	calorie, cal (4.184 J)

(unit conversion problems)

Uncertainty in Measurements

Precision: reproducibility of a measurement (scatter/random errors)

Accuracy: closeness of the measured value to the true or accepted value (bias/systematic errors); the correctness of a measurement

Expressing Uncertainty using Significant Figures

(see board)

The number of significant figures for a number tells us the precision of that number.

The number of significant figures for a number is the number of certain digits plus one (the last digit is uncertain).

Example:

Using Significant Figures in Calculations

Rules for counting significant figures:

1. Nonzero digits are always significant.

2. Zeros

a) Leading zeros precede all of the nonzero digits. They are not significant.

0.034 has ____ sig. fig.

3.4 X 10^-2

b) Captive zeros are between nonzero digits. They are always significant.

704 has _____ sig. fig.

7.04 X 10²

c) Trailing zeros follow the nonzero digits. They are significant if the number contains a decimal point.

2.0 X 10¹ ___sig. fig.

2 X 10¹___sig. fig.

20. ___sig. fig.

20 ___sig. fig.

3. Exact numbers have an infinite number of sig. fig.

numbers obtained by counting:

2 molecules

certain relationships between numbers: 100 cm = 1 m

Rules for Sig. Fig. in Mathematical Operations

1. Multiplication & Division: The number of sig. fig. in a product or a quotient is equal to the number of sig. fig. in the ________________ measurement used in the calculation.

1.78 X 54 =

2. Addition & Subtraction: the result has the same number of ____________ as the ______________ measurement in the calculation.

(see board)