2.3 Atomic Theories2.3 Atomic Theories

Greeks (5Greeks (5thth Century B.C.) Century B.C.) – coined the term – coined the term “atoms” to describe invisible particles of which “atoms” to describe invisible particles of which substances were composedsubstances were composed

Aristotle (3Aristotle (3rdrd Century B.C.) Century B.C.) – believed the – believed the universe was made of only 4 substances: universe was made of only 4 substances:

Earth, Air, Water and FireEarth, Air, Water and Fire

John Dalton (1803)John Dalton (1803) – Atomic Theory of Matter – Atomic Theory of Matter Matter composed of indivisible particles called atomsMatter composed of indivisible particles called atoms Elements contain identical atomsElements contain identical atoms Different elements contain different atomsDifferent elements contain different atoms Atoms can combine from two or more elements to Atoms can combine from two or more elements to

form new substancesform new substances

J.J. Thompson (1897)J.J. Thompson (1897) – atoms contained – atoms contained negatively charged particles called electrons; negatively charged particles called electrons; envisioned a positive sphere with embedded envisioned a positive sphere with embedded electrons; sphere had a net charge of “zero”; electrons; sphere had a net charge of “zero”; termed the “Raisin Bun” Modeltermed the “Raisin Bun” Model

H.Nagaoka (1904)H.Nagaoka (1904) – envisioned a positive – envisioned a positive sphere with a ring of electrons orbiting it (similar sphere with a ring of electrons orbiting it (similar to the rings of Saturn)to the rings of Saturn)

Ernest Rutherford (1914)Ernest Rutherford (1914) – envisioned a very – envisioned a very small positively charged nucleus surrounded by small positively charged nucleus surrounded by electrons; nucleus consisted of 1/1000electrons; nucleus consisted of 1/1000 thth of the of the total space of the atomtotal space of the atom

Niels Bohr (1921)Niels Bohr (1921) – used Rutherford’s nuclear – used Rutherford’s nuclear model with electrons ‘quantized’ in specific model with electrons ‘quantized’ in specific energy levels; became known as the Bohr-energy levels; became known as the Bohr-Rutherford Model (looked similar to planets Rutherford Model (looked similar to planets orbiting the Sun)orbiting the Sun)

Erwin Schrodinger (1926)Erwin Schrodinger (1926) - Quantum - Quantum Mechanics Theory – electrons were not in Mechanics Theory – electrons were not in definite places, rather in “probability clouds”; definite places, rather in “probability clouds”; similar to rotating fan bladessimilar to rotating fan blades

James Chadwick (1932)James Chadwick (1932) – nucleus of the atom – nucleus of the atom contained neutral particles called “neutrons”; contained neutral particles called “neutrons”; had the same mass as protons and shared the had the same mass as protons and shared the nucleus with them nucleus with them

IsotopesIsotopes

Frederick Soddy (1913) – discovered the Frederick Soddy (1913) – discovered the existence of isotopesexistence of isotopes

Isotopes are a form of the same element in Isotopes are a form of the same element in which the number of protons and electrons is the which the number of protons and electrons is the same, but the number of neutrons is different same, but the number of neutrons is different (example: carbon-12 and carbon-13) (example: carbon-12 and carbon-13)

In other words, isotopes have the same atomic In other words, isotopes have the same atomic number but different atomic massnumber but different atomic mass

atomic naturalatomic natural #p #e #n mass abundance#p #e #n mass abundance

Carbon-12 6 6 6 12 98.89%Carbon-12 6 6 6 12 98.89%Carbon-13 6 6 7 13 1.11%Carbon-13 6 6 7 13 1.11%

Average atomic mass: 12.011Average atomic mass: 12.011 a.m.u.a.m.u.

Bromine-79 35 35 44 79 50.69%Bromine-79 35 35 44 79 50.69%Bromine-81 35 35 46 81 49.31% Bromine-81 35 35 46 81 49.31%

Average atomic mass: 79.904 a.m.u.Average atomic mass: 79.904 a.m.u.

Bohr’s Theory of Atomic StructureBohr’s Theory of Atomic StructureEach electron in an atom have a fixed amount of Each electron in an atom have a fixed amount of energy related to the circular orbit in which it is energy related to the circular orbit in which it is foundfound

Electrons cannot exist between orbits, but they Electrons cannot exist between orbits, but they can move into unfilled orbits if a “quantum” of can move into unfilled orbits if a “quantum” of energy is absorbed or releasedenergy is absorbed or released

The higher the energy level, the further it is from The higher the energy level, the further it is from the nucleusthe nucleus

The maximum number of electrons in the first The maximum number of electrons in the first three levels is: 2, 8, 8three levels is: 2, 8, 8

Example: aluminumExample: aluminum Atomic number: 13 (13 protons pAtomic number: 13 (13 protons p++, 13 electrons e, 13 electrons e--)) Electrons must be distributed amoungst 3 orbits around the Electrons must be distributed amoungst 3 orbits around the

nucleus using the 2,8,8 rulenucleus using the 2,8,8 rule Diagram:Diagram:

AlAl

3e- 3e- (3(3rdrd level – “valence” level) level – “valence” level) 8e- 8e- (2(2ndnd level) level) 2e-2e- (1(1stst level) level) 13p+13p+ (nucleus)(nucleus)

Formation of Monatomic IonsFormation of Monatomic Ions

Ions – atoms which have either gained or lost electrons Ions – atoms which have either gained or lost electrons to become stable; unlike atoms, ions to become stable; unlike atoms, ions alwaysalways have a net have a net charge charge

The reason atoms gain or lose electrons to become ions The reason atoms gain or lose electrons to become ions is to attain a filled outermost (valence) shellis to attain a filled outermost (valence) shell

Metals typically lose electrons to become positively Metals typically lose electrons to become positively charged (+); while non-metals typically gain electrons to charged (+); while non-metals typically gain electrons to become negatively charged (-)become negatively charged (-)

We will limit our discussion to the first 20 elements for We will limit our discussion to the first 20 elements for simplicity reasonssimplicity reasons

Metal Ions Metal Ions Group 1 metals (e.g. Li, Na, K) donate one valence Group 1 metals (e.g. Li, Na, K) donate one valence electron to become +1 ionselectron to become +1 ions donates to a non-metaldonates to a non-metal to become…to become…

E.g. sodium atomE.g. sodium atom sodium ion sodium ion 1e- 1e- (3(3rdrd level) level)

8e- 8e- (2(2ndnd level) level) 8e-8e-

2e-2e- (1(1stst level) level) 2e-2e-

11p+11p+ (nucleus) 11p+ (nucleus) 11p+

NetNet

Charge: 0Charge: 0 +1 +1

Symbol: Na NaSymbol: Na Na++

Metal Ions Metal Ions Group 2 metals (e.g. Be, Mg, Ca) donate two valence Group 2 metals (e.g. Be, Mg, Ca) donate two valence electrons to become +2 ionselectrons to become +2 ions donates to a non-metaldonates to a non-metal to become…to become…

E.g. magnesium atomE.g. magnesium atom magnesium ion magnesium ion 2e- 2e- (3(3rdrd level) level)

8e- 8e- (2(2ndnd level) level) 8e-8e-

2e-2e- (1(1stst level) level) 2e-2e-

12p+12p+ (nucleus) 12p+ (nucleus) 12p+

NetNet

Charge: 0Charge: 0 +2 +2

Symbol: Mg MgSymbol: Mg Mg2+2+

Transition MetalsTransition MetalsTransition metals (groups 3-12) are very Transition metals (groups 3-12) are very different from other metals in that their different from other metals in that their charges are much less predictable and charges are much less predictable and often can have more than one ion charge often can have more than one ion charge (e.g. copper ions - Cu(e.g. copper ions - Cu++, Cu, Cu2+2+))

Metal Ions Metal Ions Group 13 metals (e.g. Al) donate three valence electrons Group 13 metals (e.g. Al) donate three valence electrons to become +3 ionsto become +3 ions donates to a non-metaldonates to a non-metal to become…to become…

E.g. aluminum atomE.g. aluminum atom aluminum ion aluminum ion 3e- 3e- (3(3rdrd level) level)

8e- 8e- (2(2ndnd level) level) 8e-8e-

2e-2e- (1(1stst level) level) 2e-2e-

13p+13p+ (nucleus) 13p+ (nucleus) 13p+

NetNet

Charge: 0Charge: 0 +3 +3

Symbol: Al AlSymbol: Al Al3+3+

A note about Group 14A note about Group 14

Since there are no metals in group 14 Since there are no metals in group 14 within the first 20 elements, we will move within the first 20 elements, we will move our discussion to our discussion to non-metalsnon-metals

Note: There are 3 metals in group 14 Note: There are 3 metals in group 14 beyond the first 20 elements (Ge, Pb, Sn); beyond the first 20 elements (Ge, Pb, Sn); however, their ion charges are somewhat however, their ion charges are somewhat unpredictable. We will treat them similar to unpredictable. We will treat them similar to the transition metals and look up their the transition metals and look up their charges instead of trying to predict themcharges instead of trying to predict them

Non-metal Ions Non-metal Ions Group 15 non-metals (e.g. N, P) accept three valence Group 15 non-metals (e.g. N, P) accept three valence electrons to become -3 ionselectrons to become -3 ions accepts electrons from a metal to becomeaccepts electrons from a metal to become……

E.g. phosphorus atomE.g. phosphorus atom phosph phosphideide ion ion 5e- 5e- (3(3rdrd level) level) 8e- 8e- 8e- 8e- (2(2ndnd level) level) 8e-8e- 2e-2e- (1(1stst level) level) 2e-2e- 15p+15p+ (nucleus) 15p+ (nucleus) 15p+ NetNetCharge: 0Charge: 0 -3 -3

Symbol: P PSymbol: P P3-3-

Non-metal Ions Non-metal Ions Group 16 non-metals (e.g. O, S, Se) accept two valence Group 16 non-metals (e.g. O, S, Se) accept two valence electrons to become -2 ionselectrons to become -2 ions accepts electrons from a metal to becomeaccepts electrons from a metal to become……

E.g. sulfur atomE.g. sulfur atom sulf sulfideide ion ion 6e- 6e- (3(3rdrd level) level) 8e- 8e- 8e- 8e- (2(2ndnd level) level) 8e-8e- 2e-2e- (1(1stst level) level) 2e-2e- 16p+16p+ (nucleus) 16p+ (nucleus) 16p+ NetNetCharge: 0Charge: 0 -2 -2

Symbol: S SSymbol: S S2-2-

Non-metal Ions Non-metal Ions Group 17 non-metals (e.g. F, Cl, Br, I) accept one Group 17 non-metals (e.g. F, Cl, Br, I) accept one valence electron to become -1 ionsvalence electron to become -1 ions accepts an electron from a metal to becomeaccepts an electron from a metal to become……

E.g. chlorine atomE.g. chlorine atom chlor chlorideide ion ion 7e- 7e- (3(3rdrd level) level) 8e- 8e- 8e- 8e- (2(2ndnd level) level) 8e-8e- 2e-2e- (1(1stst level) level) 2e-2e- 17p+17p+ (nucleus) 17p+ (nucleus) 17p+ NetNetCharge: 0Charge: 0 -1 -1

Symbol: Cl ClSymbol: Cl Cl --

Noble Gases Noble Gases Group 18 elements (e.g. He, Ne, Ar, Kr, Xe, Rn) were Group 18 elements (e.g. He, Ne, Ar, Kr, Xe, Rn) were “born happy” will a filled outermost shell and therefore do “born happy” will a filled outermost shell and therefore do not react with anyonenot react with anyone

E.g. argon atomE.g. argon atom 8e- 8e- (3(3rdrd level) level)

8e- 8e- (2(2ndnd level) level)

2e-2e- (1(1stst level) level)

18p+18p+ (nucleus) (nucleus)

A note about hydrogen… A note about hydrogen… Hydrogen is unique in that it can either GAIN or LOSE an electron to Hydrogen is unique in that it can either GAIN or LOSE an electron to become stablebecome stable donates to a non-metal to become…donates to a non-metal to become…

E.g. hydrogen atomE.g. hydrogen atom hydrogen ion hydrogen ion e-e- (1(1stst level) level) p+p+ (nucleus) p+ (nucleus) p+ Charge: 0Charge: 0 +1 +1 Symbol: H HSymbol: H H+ +

accepts an electron from a non-metal to become…accepts an electron from a non-metal to become…

E.g. hydrogen atomE.g. hydrogen atom hydr hydride ide ionion e-e- (1(1stst level) level) 22e-e- p+p+ (nucleus) p+ (nucleus) p+ Charge: 0Charge: 0 -1 -1 Symbol: H H Symbol: H H - -

HomeworkHomework

Worksheet #4.Worksheet #4.

Ionic CompoundsIonic Compounds

Ionic compoundsIonic compounds are formed when are formed when metals donate electrons to non-metalsmetals donate electrons to non-metals

Metals are left with a positive charge and Metals are left with a positive charge and are called are called cations cations (e.g. Na(e.g. Na++, Mg, Mg2+2+ ) )

Non-metals are left with a negative charge Non-metals are left with a negative charge and are called and are called anions anions (e.g. Cl(e.g. Cl--, N, N3-3-))

Ionic CompoundsIonic CompoundsGroup 1 elements (Li, Na, K) react very readily with Group 17 Group 1 elements (Li, Na, K) react very readily with Group 17 elements (F, Cl, Br, I) because an exchange of one electron results elements (F, Cl, Br, I) because an exchange of one electron results in both ions having a filled outermost shell; e.g. in both ions having a filled outermost shell; e.g.

sodium (atom) + chlorine (atom) sodium (ion) + chlorsodium (atom) + chlorine (atom) sodium (ion) + chlorideide (ion) (ion) NaNa ClCl Na Na ++ Cl Cl --

e- e- 7e-7e- 8e-8e- 8e- 8e- 8e-8e- 8e- 8e- 8e-8e- 2e-2e- 2e-2e- 2e-2e- 2e-2e- 11p+11p+ 17p+17p+ 11p+11p+ 17p+17p+

Ionic CompoundsIonic CompoundsGroup 2 elements (Be, Mg, Ca) react very readily with Group 16 Group 2 elements (Be, Mg, Ca) react very readily with Group 16 elements (F, Cl, Br, I) because an exchange of two electrons results elements (F, Cl, Br, I) because an exchange of two electrons results in both ions having a filled outermost shell; e.g. in both ions having a filled outermost shell; e.g.

calcium (atom) + oxygen (atom) calcium (ion) + oxcalcium (atom) + oxygen (atom) calcium (ion) + oxideide (ion) (ion) CaCa O O Ca Ca 2+2+ O O 2-2-

2e- 2e- 8e-8e- 8e-8e- 8e- 8e- 6e-6e- 8e- 8e- 8e-8e- 2e-2e- 2e-2e- 2e-2e- 2e-2e- 20p+20p+ 8p+8p+ 20p+20p+ 8p+8p+