Chapter 2

Matter Consists of ElementsElements cannot be

broken down by ordinary chemical meansAtoms are unique building

blocks for each elementAtomic structure

CompoundA substance consisting of

two or more different elements combined in a fixed ratio

Ex. (C6H12O6)

Atomic StructureThere are three important subatomic particles in

atomsNeutrons

No charge in the nucleus1 atomic mass unit (amu)

Protons Positive charge, in the nucleus 1 amu

ElectronsNegative charge , orbit nucleus

Zero amuEqual in number to protons in atom

Atoms of different elements contain different numbers of subatomic particlesCompare hydrogen, helium and lithium

Figure 2.2

Proton

Neutron

Electron

Helium (He) Lithium (Li)Hydrogen (H)

Atomic Number and Atomic MassAtomic number = number of protons in

nucleusMass number = mass of protons and

neutronsMass numbers of atoms of an element: are not all identical

Isotopes: atoms of the same element that differ in the # of neutrons they contain

Proton

Neutron

Electron

Deuterium (2H) Tritium (3H)Hydrogen (1H)

Isotopes

Radioactive Isotopes can Help or Harm Us

The Distribution of Electrons Determines an Atoms Chemical Properties

Electrons occupy up to seven electron shells (energy levels) around nucleus

Octet rule: Except for the first shell which is full with two electrons, atoms interact in order to have eight electrons in their outermost energy level (valence shell)Stable elements have their valence shell fully

occupiedReactive elements lack a full valence shell and

tend to gain, lose, or share electrons (form bonds) with other atoms to achieve stability

Helium (He) Neon (Ne)

2e 2e8e

(a) Chemically inert elements

Valence shell complete

2e4e

2e8e

1e

(b) Chemically reactive elementsValence shell incomplete

Hydrogen (H) Carbon ©

1e

Oxygen (O)Sodium (Na)

2e6e

Covalent Bonds join atoms into molecules through electron sharing

Three Important Types of Chemical BondsCovalent, Ionic and Hydrogen

Covalent BondsFormed when atoms share two or more

valence shell electrons Molecule = two or more atoms held together

by covalent bondsAllows each atom to fill its valence shell

at least part of the timeSharing of electrons can be equal or

unequal Equal sharing produces electrically balanced,

nonpolar molecules Ex. CO2

Unequal sharing by atoms with different electron-attracting abilities produces polar molecules Ex. H2O

Atoms with six or seven valence shell electrons are electronegative, e.g., oxygen

Ionic bonds are attractions between ions of opposite charge

Ions are formed by: transfer of valence shell electrons between atomsAnions (– charge): have gained one or more electronsCations (+ charge): have lost one or more electrons

Attraction of opposite charges: results in an ionic bond

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

Sodium chloride (NaCl)

+–

(a) The slightly positive ends (+) of the watermolecules become aligned with the slightlynegative ends (–) of other water molecules.

+

–

–

–– –

+

+

+

+

+

Hydrogen bond

Attractive force between

electropositive hydrogen of one molecule and an

electronegative atom of another molecule

Hydrogen Bonds

Properties of WaterChargedExists as Gas, Liquid

and SolidUniversal solventAdhesion and Cohesion

(via H-bonds)Surface tensionIonizes into acid and

base

CohesionWater binding to water

AdhesionWater binding to anything that

has a charge Remember water has a charge

and thus will bind to anything with a charge

Properties of Water