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Atoms, Elements, Compounds, and Chemical Bonds: Essential Concepts for General Chemistry

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States of Matter

Solids, Liquids, and Gases

Understanding the three primary states of matter is fundamental in chemistry. Each state is characterized by distinct physical properties:

  • Solids: Have a fixed shape and volume.

  • Liquids: Have a fixed volume but assume the shape of their container.

  • Gases: Have neither fixed shape nor volume; they expand to fill their container.

Physical vs. Chemical Changes

Changes in matter can be classified as physical or chemical:

  • Physical Change: Alters the state or appearance of matter without changing its composition. Example: Water freezing to ice.

  • Chemical Change: Involves the rearrangement of atoms, resulting in new substances. Example: Combustion of hydrogen to form water.

Classification of Matter

Types of Matter

Matter is anything that occupies space and has mass. It can be classified as:

  • Atoms: The basic units of matter.

  • Elements: Pure substances consisting of only one type of atom.

  • Molecules: Groups of atoms bonded together.

  • Compounds: Substances formed from two or more elements chemically bonded.

  • Mixtures: Physical combinations of two or more substances.

Atoms and Elements

Atomic Structure

Atoms consist of protons, neutrons, and electrons:

  • Protons: Positively charged particles in the nucleus.

  • Neutrons: Neutral particles in the nucleus.

  • Electrons: Negatively charged particles orbiting the nucleus.

The number of protons defines the element (atomic number), and in a neutral atom, the number of electrons equals the number of protons.

Atomic Mass and Isotopes

Atomic mass is the sum of protons and neutrons. Isotopes are atoms of the same element with different numbers of neutrons.

  • Example: Neon has three isotopes: Ne-20, Ne-21, Ne-22.

Average atomic mass is calculated using the natural abundance of each isotope:

Sample Calculation

For Neon:

  • Ne-20: 90.48%

  • Ne-21: 0.27%

  • Ne-22: 9.25%

Periodic Table and Ionic Charge Trends

Periodic Table Overview

The periodic table organizes elements by increasing atomic number and groups elements with similar properties.

Periodic Table of the Elements

Ionic Charge Trends

Elements tend to form ions with characteristic charges based on their group in the periodic table:

  • Group 1: +1

  • Group 2: +2

  • Group 13: +3

  • Group 15: -3

  • Group 16: -2

  • Group 17: -1

  • Group 18: 0 (noble gases)

Trends for Ionic Charge

Chemical Bonds

Ionic and Covalent Bonds

Chemical bonds are the forces holding atoms together in compounds:

  • Ionic Bonds: Formed between metals and nonmetals by transfer of electrons.

  • Covalent Bonds: Formed between nonmetals by sharing electrons.

Formulas and Naming Compounds

Compounds are represented by chemical formulas. Naming conventions differ for ionic and molecular compounds:

  • Ionic Compounds: Name of metal (or transition metal with Roman numeral for charge) + name of nonmetal (ending in "-ide") or polyatomic ion.

  • Molecular Compounds: Prefix + name of first nonmetal, prefix + name of second nonmetal (ending in "-ide"). The prefix "mono" is not used for the first element.

Numerical Prefixes for Molecular Compounds

Prefixes indicate the number of atoms in molecular compounds:

Number

Prefix

Number

Prefix

Number

Prefix

1

mono

5

penta

9

nona

2

di

6

hexa

10

deca

3

tri

7

hepta

11

undeca

4

tetra

8

octa

12

dodeca

Numerical Prefixes Table

Polyatomic Ions

Common Polyatomic Ions

Polyatomic ions are charged groups of covalently bonded atoms. Familiarity with their names and formulas is essential for naming compounds:

Name

Formula

Name

Formula

ammonium

NH4+

nitrate

NO3-

acetate

CH3COO-

nitrite

NO2-

carbonate

CO32-

hypochlorite

ClO-

phosphate

PO43-

chlorite

ClO2-

hydroxide

OH-

chlorate

ClO3-

sulfate

SO42-

perchlorate

ClO4-

sulfite

SO32-

cyanide

CN-

Common Polyatomic Ions Table

Empirical and Molecular Formulas

Determining Formulas

The empirical formula shows the simplest ratio of elements in a compound, while the molecular formula gives the actual number of atoms of each element in a molecule.

  • Example: Benzene's molecular formula is C6H6, empirical formula is CH.

To determine the molecular formula:

  1. Calculate the empirical formula mass.

  2. Divide the molar mass by the empirical formula mass to find the multiplier (N).

  3. Multiply the empirical formula by N.

Avogadro's Number and Moles

Avogadro's Number

One mole of any substance contains particles (atoms, molecules, or ions).

Scientific Notation and Metric Prefixes

Metric Prefixes

Metric prefixes are used to express quantities in scientific notation:

Prefix

Symbol

Value

Scientific Notation

exa

E

1,000,000,000,000,000,000

1018

peta

P

1,000,000,000,000,000

1015

tera

T

1,000,000,000,000

1012

giga

G

1,000,000,000

109

mega

M

1,000,000

106

kilo

k

1,000

103

hecto

h

100

102

deka

da

10

101

--

--

1

100

deci

d

0.1

10-1

centi

c

0.01

10-2

milli

m

0.001

10-3

micro

μ

0.000001

10-6

nano

n

0.000000001

10-9

pico

p

0.000000000001

10-12

femto

f

0.000000000000001

10-15

atto

a

0.000000000000000001

10-18

Metric Prefixes Table

Summary Table: Atoms, Elements, Molecules, Compounds, Mixtures

Type

Atoms

Elements

Molecules

Compounds

Mixture

A

3

1

0

0

No

B

9

3

3

3

Yes

C

6

1

3

0

No

Additional info:

  • Some content was inferred and expanded for clarity and completeness, such as definitions and formula derivations.

  • Tables were recreated and expanded for academic context.

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