Atomic Structure / Periodic Table (Chpt



Atomic Structure / Periodic Table

Historical Atomic Models

A. Early Greek:

1. Democritus (≈400 BC) Called small particles “atoms” from Greek word ATOMOS means “indivisible” or “uncut.”

2. Aristotle’s Model (≈300 BC) - matter made up of fire, air, earth, water. No limit to how matter is divided.

B. John Dalton’s Model (1808) – atoms are solid spheres like billiard balls.

C. J.J. Thomson’s Model (1897) – atoms are positive spheres embedded with negatively-charged particles called electrons. (Watermelon model – red flesh is positive part, seeds are the electrons).

D. Lord Ernest Rutherford’s Model (1911):

1. Used Thomson’s model in a “Gold Foil” experiment where he used a path of positive particles bombarding through a thin sheet of gold foil surrounded with film. Experiment proved Thomson’s model false – something else is inside the atom (nucleus).

2. Atoms are mostly empty space and contain a tiny, dense, (+) nucleus and electrons.

E. Niels Bohr’s Model (1913): Worked with Rutherford and found electrons orbit around nucleus but not in set pathways. His model is still used to diagram atoms.

F. Electron Cloud / Quantum Models: Current models refer to a nucleus with surrounding electron energy levels. To move from one energy level to another, an electron needs a packet of energy (quantum).

Subatomic Particles: Protons, Electrons (e-), Neutrons, Quarks

A. Nucleus is made up of protons (+) and neutrons (0).

B. Most of the mass of an atom is made up of the protons in the nucleus. (Electrons have almost NO mass.)

C. Atomic Number: number of protons in an element. (# of Protons = # of electrons. Atoms as a whole are neutral.)

D. Quarks – smaller particles making up protons and neutrons.

E. Changes of atomic nuclei:

1. Half-life: time required for one half of a sample of a radioisotope (any atom with an unstable nucleus) to decay.

2. Fusion: a nuclear reaction in which the nuclei of two atoms combine to form a larger nucleus (the sun).

3. Fission: a nuclear reaction in which an atomic nucleus is split into two smaller parts.

Energy Levels of an Atom

A. Electrons orbit within energy levels.

1. Electrons in energy levels close to the nucleus have low energy.

2. Electrons in outside energy levels have high energy.

B. Each energy level has a maximum number of electrons it can hold. Examples:

1. 1st energy level (K) can hold up to 2 e-.

2. 2nd energy level (L) can hold up to 8 e-.

3. 3rd energy level (M) can hold up to 18 e- IF it is NOT the outermost energy level.

4. 4th energy level (N) can hold up to 32 e- IF it is NOT the outermost energy level.

C. The # of energy levels of an atom depends on the # of e-. Example:

1. Hydrogen has 1 e- with only 1 energy level (K).

2. Helium has 2 e- with 1 energy level since the 1st level (K) can hold 2 e-.

3. Lithium has 3 e- in 2 energy levels: 2 e- in (K) and 1 e- in (L).

4. Magnesium has 12 e- in 3 energy levels: 2e- in (K), 8 e- in (L), and 2 e- in (M).

D. The electrons found in the outermost energy level are called valence electrons.

E. **The outermost energy level can never have more than 8 e- even if that energy level can hold more than 8 e-!

I. Bohr model examples: examples from overhead.

II. Organization of the Periodic Chart

A. Dmitri Mendeleev (1871), a Russian chemist arranged the elements in the first periodic table.

1. Elements were arranged by atomic mass and found that similar properties occurred over and over.

2. He was able to predict properties of unknown elements at that time.

B. Today’s periodic chart is similar to Mendeleev’s but the atoms are arranged by increasing atomic numbers.

C. Elements in each column have the same number of valence electrons (e- in the outermost energy level)

D. Roman Numerals I-VIIIA indicate the number of valence electrons present. Examples:

1. H and Li in IA have only 1 valence e-.

2. C and Si in IVA have 4 valence e-.

3. Ne and Kr in VIIIA have 8 valence e-.

E. Each of the 18 columns (vertical) form a group or family of elements that have similar physical and chemical properties.

F. Each of the 7 rows (horizontal) form a period of elements. Elements in a period are arranged by increasing atomic numbers and do NOT have similar properties.

III. Group / Family characteristics:

A. Alkali Metals: Found in group 1 (IA)

1. Include Li, Na, K, Rb, Cs, Fr.

2. Have one valence (e-).

3. Soft, silvery white metals.

4. React readily with other elements.

5. Never found in a free state in nature.

B. Alkaline Earth Metals: Found in group 2 (IIA)

1. Include Be, Mg, Ca, Sr, Ba, Ra.

2. Have 2 valence (e-).

3. React readily with other elements.

4. Rarely found in a free state in nature.

C. Halogens: Found in group 17 (VIIA)

1. Include F, Cl, Br, I, At.

2. Have 7 valence (e-).

3. React with alkali metals to form salts. Ex: Na (alkali metal) combines with Cl (halogen) to form table salt (NaCl).

D. Noble (Inert) Gases: Found in group 18 (VIIIA)

1. Include He, Ne, Ar, Kr, Xe, Rn.

2. Outer energy levels are filled (very stable).

3. Inert gases – don’t readily react.

4. Found in a free state in nature.

IV. Weights, Masses, and Numbers:

A. Atomic Mass Unit (AMU) – mass units:

Mass of 1 proton = 1 AMU

Mass of 1 neutron = 1 AMU

B. Mass Number (NOT found on the periodic chart) – sum of the mass of protons and neutrons in the nucleus. The units are in AMU’s (# protons + # neutrons = mass #)

C. Isotope – atoms of the same element having different atomic masses (due to different numbers of neutrons). Ex.: isotope of iodine: I-131 or

Superscript 131 is the mass # and subscript 53 is atomic #. The exact # of neutrons can be found by subtracting the atomic # from the mass #: 131 – 53 = 78 neutrons. There are 78 N in this isotope.

D. Atomic Mass (Atomic Weight) – AVERAGE of the mass # of all naturally occurring isotopes.

E. Atomic # - # of protons (also the # of e-).

F. To find the AVG. # N:

V. Organization of metals / nonmetals:

A. Metals:

1. All elements (except H) found on the LEFT side of the stair-step division on the periodic table.

2. General properties:

a. Good conductors of heat / electricity

b. Malleable

c. Ductile

d. Have luster

e. Solid

B. Nonmetals:

1. Elements found on the RIGHT side of the stair-step division (plus H) on the periodic table.

2. General properties:

a. Poor conductors of heat / electricity

b. Dull in appearance

c. Not malleable

d. Gas, liquid, or crystalline state

C. Metalloids:

1. Elements next to the stair-step line.

2. Have some properties of metals & nonmetals.

3. Examples: B and Si.

D. Transition Elements:

1. Elements in Groups 3 through 12.

2. Metals, but have properties not found in elements of other groups.

3. Examples: Cu and Fe.

E. Rare Earth Elements: Lanthanide & Actinide Series: Metals, belong to 3rd group /periods 6 & 7.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download