All Matter Consists of Elements• Chemistry is the study of matter• Matter is

– Anything that has mass and occupies space– Composed of elements

• Elements– Cannot be broken down to a simpler form– Periodic table of elements – lists all known

elements

Figure 2.2

Groupnumber

Atomicnumber

Element symbol

Atomic mass

Nonmetals

Metals

Transition elements

Lanthanides

Actinides

Metals Nonmetals

Atoms – Smallest Functional Unit of Elements

• Atoms consist of– Nucleus (central core)

• Protons– positive charge– have mass

• Neutrons– no charge– have mass

– Shells (surrounding nucleus)• Electrons

– negative charge– no discernable mass

Figure 2.3

Electron

Proton

Shell

Neutron

Nucleus

a) Hydrogen 1 proton

b) Oxygen 8 protons 8 neutrons 8 electrons in 2 shells

c) Sodium 11 protons 11 neutrons 11 electrons in 3 shells

More About Atoms• Atomic symbol: one or two letters

– Na: sodium– O: oxygen

• Atomic number– Number of protons

• Atomic mass– Roughly equal to number of protons plus neutrons

• In an electrically neutral atom– Number of protons = number of electrons

Isotopes Have a Different Number of Neutrons

• Same atomic number (same number of protons)

• Different atomic mass (different number of neutrons)

• Unstable isotopes are called radioisotopes• Radioisotopes give off

– Energy (in the form of radiation)– Particles

• Unstable isotopes are called radioisotopes– Give off energy in the form of radiation

• Some radioisotopes have scientific and medical uses– Carbon-14: used for dating fossils– Diagnostic imaging– Cancer treatment– Power supply for implants such as cardiac

pacemakers

Isotopes Have a Different Number of Neutrons

Energy Fuels Life’s Activities

• Energy: the capacity to do work• Potential energy: stored energy• Kinetic energy: energy in motion,

doing work• Potential energy can be transformed into

kinetic energy

Energy Fuels Life’s Activities

• Electrons have potential energy– Each shell corresponds to a specific level of

potential energy– Shells that are farther from the nucleus contain

electrons with more potential energy

• Atoms are most stable when their outermost shell is full

• Atoms will interact with other atoms to fill their outermost shells

Chemical Bonds Link Atoms to Form Molecules

• Chemical bonds: attractive forces holding atoms together

• Kinds of chemical bonds– Covalent bonds– Ionic bonds– Hydrogen bonds

Covalent Bonds• Covalent bonds form when atoms share

electrons • Very strong bonds• Examples

– Hydrogen molecule: H2

– Oxygen molecule: O2

– Water: H2O

Figure 2.5

Writtenformula Structural representation

Structuralformulawithcovalentbond

Hydrogen(H2)

Oxygen

(O2)

Water(H2O)

Two singlecovalent bonds

Single covalent bond

Double covalent bond

Covalent Bonds• Nonpolar covalent bonds: electrons are

shared equally– H2

– O2

– CH4

• Polar covalent bonds: electrons are NOT shared equally– H2O: The oxygen has a stronger pull on the

shared electrons than the hydrogen does

Ionic Bonds• Ion: an electrically charged atom or

molecule• Positively charged ion: forms if an atom or

molecule loses electrons• Negatively charged ion: forms if an atom or

molecule gains electrons• Ionic bond: attractive force between

oppositely charged ions• Example: NaCl

Figure 2.6

Loss of electron:positive charge

Gain of electron:negative charge

Sodium atom (Na) Chlorine atom (Cl) Sodium ion (Na+)

Sodium chloride molecule (NaCl)

Chloride ion (Cl–)

Hydrogen Bonds• Form between polar molecules• Polar molecules

– Contain polar covalent bonds in which there is unequal sharing of electrons

– Electrically neutral overall, but uneven charge distribution

• Hydrogen bond – Weak attraction between oppositely charged

regions of polar molecules – Example: weak forces between water

molecules

Figure 2.7

Molecule

Oxygen (O)

Hydrogen (H)

Water Ice

Life Depends on Water

• Water molecules are polar

• Water is liquid at body temperature• Water is the biological solvent

• Water can absorb and hold heat energy• Water helps regulate body temperature

Water Is the Biological Solvent• Solvent: liquid in which other substances

dissolve• Solute: any dissolved substance• Hydrophilic: polar molecules that are

attracted to water and interact easily with water

• Hydrophobic: nonpolar neutral molecules that do not interact with or dissolve in water

Figure 2.8

Ionsin solution

Moleculesof water

Salt crystal

The Importance of Hydrogen Ions

• Acids:– Donate hydrogen ions (protons)– Increase hydrogen ion concentration in

solutions

• Bases – Accept hydrogen ions (protons)– Lower hydrogen ion concentration in solutions

• pH Scale– A measure of hydrogen ion concentration

The pH Scale

• Measure of hydrogen ion concentration in solution

• Ranges from 0 to 14– Acids: pH < 7– Neutral: pH = 7– Basic: pH > 7

pH values

Concentrationsof H+

(moles/liter)Drain opener

Bleach

Ammonia cleanser

Soapy water

Baking soda

Human blood, tears

Saliva, urine

Black coffee

Tomatoes

Vinegar, cola

Lemon juice

Hydrochloric acid

Concentrated nitric acid

Mo

re a

cid

ic

Neutral pH

Mo

re a

lkal

ine

14

13

12

11

10

9

8

7

6

5

4

3

2

1

10–13

10–11

10–9

10–7

10–5

10–3

10–1

0Figure 2.10

Buffers

• Minimize pH change• Help maintain stable pH in body fluids• Carbonic acid and bicarbonate act as one of

the body’s most important buffer pairs• HCO3

- + H+ H2CO3

Water and Chemistry