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