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The Hydrogen AtomThe Hydrogen Atom

Other AtomsOther Atoms

Only 2 electrons fit in the lower shell.The 3rd electron must fit in the next shell.

Atomic ShellsAtomic ShellsThe discrete electron levels are arranged in shells. Each shell has a maximum occupancy.

The first electronic shell can have at most 2 electrons, the second shell has room for 8 electrons and so on.

The 1st shell has the lowest energy. Thus, elements, in their lowest energy state fill the 1st level first, and then fill the 2nd level next. These elements are listed in the 1st and 2nd rows of the periodic table.

Atoms are most stable if their outer shell is full.

The electrons in outer shells are shielded by the inner shells from the full attraction of the nucleus. These electrons participate most readily in chemical reactions.

Atomic ShellsAtomic Shells

How many electrons does neutral Carbon (6 protons) have in its outer shell?

How many electrons does neutral Neon (10 protons) have in its outer shell?

The Periodic TableThe Periodic Table

Atomic Atomic SizesSizes

IonizatioIonization Energyn Energy

Periodic or Mendelev TablePeriodic or Mendelev Table

Li: solid, Cs: liquid, Ar: gas, Tc:Tc: synthetic

# protons

1 e- in outer shell (Alkali Metals) Full outer shell (Noble Gases)

1 e- missing to fill shell (Halogens)

BondingBonding

There are three major ways that elements bond to form molecules.

Ionic BondsIonic BondsAtoms with filled shells, the Noble Gases, are highly inert.

Atoms with one electron in the outer shell, and atoms with one electron missing are, on the other hand, highly reactive. These atoms form ionic bonds. The alkali gives up an electron. The halogen takes the electron. Elements are bonded by the electric force between the ions.

Example of ionic bondsExample of ionic bonds

Ruby

Sapphire

Aluminum oxide, Al2O3

Metallic BondsMetallic BondsAtoms in a metals also give up electrons, however the electrons are not transferred to the other atom. Instead, they are shared by all atoms.

The electron sea allows current to flow through metal. Metals thus make good conductors.

In sodium, for example, 1 out of the 11 electrons is released so that Na has two filled shells. The extra electrons move around the metal in a “sea” of negative charge. This negatively charged sea moves around a regular structure of positive Na ions.

Covalent BondsCovalent BondsCertain molecules are formed by sharing electrons. The covalent bond that forms resembles metallic bonds in that electrons are shared. Yet, like ionic bonds the electrons are shared in discrete shells of the atoms and don’t run willy nilly throughout the material.

QuestionQuestion

How would you covalently bond two oxygen atoms to make O2? Oxygen has 8 protons & electrons.

How many electrons would each O have to share with the other?


What kind of bonding does KBr have?

# protons



AnswerAnswer

QuestionQuestion

How would you expect KF to be bonded?


What kind of bonding does KBr have?

# protons



AnswerAnswer

Ionic Bond: K+F-

Multiple Multiple Covalent Covalent

BondsBonds

N278%

O221%

H2O 0-4%

Ar 0.9%

CO20.035%

Ne 0.0018%

He 0.0005%

CH40.0001%

H20.00005%

O30.000004%

Earth’s Atmosphere

Gases in Earth’s atmosphere are mainly covalently bonded molecules or noble gases.

Combining C6, N7, O8

Molecular Molecular attractionattraction

ssPolar molecules are more positively charged on one side and more negative on the other. This provides a cohesion.

Mars: why Mars: why red?red?

Iron Oxides are presentIron Oxides are presente.g. Hematite or Fe2O3

Ozone LayerOzone Layer

Life on other planetsLife on other planets

SummarySummaryAtoms have discrete energy levels, specific to that atom.Atoms have discrete energy levels, specific to that atom.A photon is absorbed when an electron jumps to a higher energy level.A photon is absorbed when an electron jumps to a higher energy level.A photon is emitted when an electron drops to a lower energy level. A photon is emitted when an electron drops to a lower energy level. The emitted/absorbed photon’s energy equals the difference between the The emitted/absorbed photon’s energy equals the difference between the

atomic levels involved. atomic levels involved. Atomic levels can only fit a certain number of electrons (2 in the 1Atomic levels can only fit a certain number of electrons (2 in the 1stst level, 8 in level, 8 in

the 2the 2nd nd …)…)The periodic table is arranged according the electronic shells and the The periodic table is arranged according the electronic shells and the

number of protons/electrons in the atom. number of protons/electrons in the atom. Atoms with filled shells are most stable. Atoms bond in order to achieve this Atoms with filled shells are most stable. Atoms bond in order to achieve this

configuration. configuration. Ionic bonding involves the transfer of electrons from one atom to another. Ionic bonding involves the transfer of electrons from one atom to another. Covalent bonding involves the sharing of electrons by one or several atoms.Covalent bonding involves the sharing of electrons by one or several atoms.Metallic bonding involves the sharing of electrons by the entire Metallic bonding involves the sharing of electrons by the entire

material/metal. material/metal.

Radioactive DatingRadioactive Dating

ParentParent

Carbon-14Carbon-14 DaughterDaughter

Nitrogen-14Nitrogen-14 Half LifeHalf Life

5,730 yrs*5,730 yrs*

Potassium-40Potassium-40 Argon-40Argon-40 1.25 billion 1.25 billion yrsyrs

Uranium-238Uranium-238 Lead-206Lead-206 4.5 billion yrs4.5 billion yrs

Thorium-232Thorium-232 Lead-208Lead-208 14 billion yrs14 billion yrs

Rubidium-87Rubidium-87 Strontium-87Strontium-87 48.8 billion 48.8 billion yrsyrs

Samarium-Samarium-147147

Neodymium-Neodymium-143143

106 billion yrs106 billion yrs

Uranium-235Uranium-235 Lead-207Lead-207 704 billion yrs704 billion yrs*Time that it takes wood to have half the C14 of a living plant.

Swisher et al. 1992, Science

Carbon Dating Carbon Dating

1. Solar neutrons enter Earth’s atmosphere.

2. Neutrons collide with N14 (7p, 7n), creating C14 (6p,8n) [n + N14 p + C14 ]

3. Living bodies continually absorb C14 (e.g. as CO2 in photosynthesis).

4. When the plant or animal dies, it no longer assimilates C14.

5. The C14 decays (half life of 5730 yrs). [C14 N14 + e- + ve ] (n p + e- + ve )

6. The e- emission rate reveals the age.

Measure ages < 70,000 yrs

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