Atoms and Elements

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Chapter 2

• Atoms and Elements

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Daltons Atomic Theory

• (beginning of 19th century)
• All matter is composed of tiny, indivisible
  particles called atoms
• All atoms of a given element are identical to
  each other and different from those of other
  elements
• A chemical reaction merely involves a change in
  the groupings of atoms and not creation or
  destruction of atoms (Law of Conservation of Mass)

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• Compounds consist of atoms of more than one
  element combined in particular ratios (Law of
  Constant Composition and Law of Multiple
  Proportions)

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Building up Atomic Structure

• Benjamin Franklin (1706-1790) discovered two
  types of electricity, () and (-).
• Henri Becquerel discovered radioactivity on 1896.
  Pierre and Marie Curie continued that work atoms
  disintegrate, i.e., they are divisible.
• John J. Thomson discovered the electron and
  determined its charge/mass ratio (1896-97).
• Robert A. Millikan (1909) determined the charge
  and mass of electron.
• Ernest Rutherford (19011-19) discovered the
  proton.
• James Chadwick (1932) discovered the neutrons,
  that are with the protons in the nucleus of atoms.

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Atomic Structure

• subatomic particles
• neutron no charge, 1.0087 amu, n
• proton 1 charge, 1.0073 amu, p
• electron 1 charge, 0.0005486 amu, e
• n and p packed tightly into dense core called
  nucleus
• e distributed more diffusely in space
  surrounding nucleus

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e
n
p
e
Actual size Radius of atom 100 pm (10-10
m) Radius of nucleus 0.001 pm Then, if radius
of atom was 100 m (a small football stadium),
the radius of the nucleus would be 0.001 m 1
mm
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Atomic number and Mass number

• all atoms of a given element have the same number
  of protons
• number of protons in an atom given by the atomic
  number, Z
• neutral atoms have same number of protons and
  electrons
• atoms gain or lose charge by gaining or losing
  electrons only (not protons)
• total number of protons and neutrons given by
  mass number, A

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Symbol
charge
mass number
n
A
X
Z
element symbol
atomic number
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Examples

• Determine the numbers of electrons, protons, and
  neutrons in each of the following atoms.

40
Ar
18
11
40
Ar
18

• Z 18, therefore 18 p
• A 40,
• A of p of
  neutrons
• Therefore, neutrons A - p
• 40 18 22 neutrons
• Charge, n 0, therefore of e 18

12
209
2
Pb
82

• Z 82, therefore 82 p
• A 209, therefore 209 p and n total
• neutrons A - p 209 82 127 n
• n 2,
• Therefore e 82 p - 2 80 e (lost 2 e)

13
31
3
P
15
14
31
3
P
15
Z 15, therefore 15 p
15
31
3
P
15
Z 15, therefore 15 p A 31, therefore 31 p
and n total
16
31
3
P
15
Z 15, therefore 15 p A 31, therefore 31 p
and n total 31 15 16 n
17
31
3
P
15
Z 15, therefore 15 p A 31, therefore 31 p
and n total 31 15 16 n n 3 , (gained 3
e) Therefore, e- 15 3 18 e-
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Isotopes

• atoms that have the same number of protons but
  different numbers of neutrons, i.e., different A
• may or may not have same number of electrons

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52
55
X
X
24
24
20
52
55
X
X
24
24
52
52
X
X
24
20
21
55
52
X
X
24
24
52
52
X
X
24
20
50
52
3
X
X
24
24
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Isotope abundance

• A sample of naturally
• occurring sulfur contains
• several isotopes with the
• following abundances
• Isotope abundance
• 32S 95.02
• 33S 0.75
• 34S 4.21
• 36S 0.02
• of
  atoms of a given isotope
• Abundance ---------------------------- x 100
• Total of atoms of
  all isotopes of element

32S, 33S, 34S, 36S 16 16 16
16
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Mass Spectrometry andIsotopic Abundances

• mass spectrometer.
• Device generates ions that pass down an evacuated
  path inside a magnet.
• Ions are separated based on their mass.

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Atomic Weight

• The atomic mass and Isotope Abundances are
• determined by means of Mass Spectrometry.
• Atomic mass of isotope carbon-12 is defined
  exactly 12
• amu whereas all others of carbon and other
  elements
• are referred to that and do not have integer
  values.
• abundance
  isotope 1
• Atomic weight ??????????? x (mass isotope 1)
• 100
• abundance isotope 2
• ??????????? x (mass isotope 2)
• 100

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Example

• Isotope abundance mass (amu)
• 64 Zn 48.6 63.9291
• 66Zn 27.9 65.9260
• 67Zn 4.1 66.9721
• 68Zn 18.8 67.9249
• 70Zn 0.6 69.9253

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Example, contd.

• 
  ?abund.i
• Atomic weight of Zn ?????? ? mi
• 
  100
• A.W. 0.486 ? 63.9291 0.279 ? 65.9260
• 0.041 ? 66.9721 0.188 ? 67.9249
• 0.006 ? 69.9253 65.4 amu

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25. Gallium has two naturally occurring
isotopes, 69Ga and 71Ga, with masses of 68.9257
amu and 70.9249 amu, respectively. Calculate the
abundance of the two isotopes of Ga. A W Ga
69.723 (Per. table)

• Lets name p1 of 69Ga and p2 of
  71Ga.
• p1 p2 100 then, p1 100 - p2
  (1)
• p1 ? 68.9257 p2 ?
  70.9249
• AW 69.723 -------------------- then,
• 100
• 6972.3 p1?68.9257 p2?70.9249 Then, replace
  p1 by (1)
• 6972.3 (100 - p2) ? 68.9257 p2 ?
  70.9249
• 6972.3 6892.57 - p2 ? 68.9257 p2 ? 70.9249
• 6972.3 - 6892.57 p2 ? (70.9249 - 68.9257)
• 6972.3 - 6892.57
• p2 ----------- 39.88 p1
  60.12
• 70.9249 - 68.9257

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Atoms and the Mole

• A collection term states
• a specific number of
• items.
• 1 dozen donuts
• 12 donuts
• 1 ream of paper
• 500 sheets
• 1 case 24 cans

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Atoms and the Mole

• A mole is (a collection number) the amount of a
• substance that contains
• the same number of particles (atoms, molecules,
  ions, protons, electrons, etc.) as there are
  carbon atoms in 12 g of carbon-12 isotope
• 1 mol 6.022 x 1023 particles (Avogadros
  number). Amadeo Avogadro
• The number is referred to the atomic mass
  assigned to carbon-12 isotope.

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Atoms and the Mole

• 1 mole of Number of particles
• 1 mole C 6.022 x 1023 C atoms
• 1 mole Na 6.022 x 1023 Na atoms
• 1 mole Au 6.022 x 1023 Au atoms
• 1 mole electrons 6.022 x 1023 electrons
• 1 mole H2O 6.022 x 1023 H2O molecules
• 1 mole Na 6.022 x 1023 Na ions

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Molar Mass

• The molar mass of any element is the mass in
• grams of 6.022 x 1023 atoms of that element,
• i.e., one mole of the element.
• Molar mass is abbreviated M, has units of
• grams per mole (g/mol), and is numerically
• equal to the atomic weight of the element.
• Molar mass of Na 22.990 g/mol
• Molar mass of Cl 35.453 g/mol
• Molar mass of O 15.999 g/mol

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Conversion factors

• Avogadros number 6.022 x 1023 can be written
  as equalities and conversion factors.
• Equality
• 1 mole 6.022 x 1023 particles molar mass
  (g)
• Conversion Factors particles atoms or
  molecules
• 6.022 x 1023 particles and 1 mole
  
• 1 mole 6.022 x 1023 particles
• 6.022 x 1023 particles and molar mass
  (g)
• molar mass (g) 6.022 x 1023 particles
• 1 mole and
  molar mass (g)
• molar mass (g) 1 mole

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Converting moles to mass and ?

• Moles to mass Mass to
  moles
• g
  1 mol
• moles x ---- grams g x ---- moles
• 1 mol
  grams
• The molar mass as conversion factors
• What is the mass of silicon represented by
• 0.250 moles of this element? M of Si 28.086
• 28.09 g
  g/mol
• 0.250 moles x ------ 7.02 g Si
• 1 mol

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• How many moles of manganese are 19.36 g of
• that metal? M of Mn 54.938 g/mol
• 1 mol
• 19.36 g x ----- 0.352384 0.3524 moles
• 54.938 g
  4 SF
• How many atoms of calcium are in 4.008 g of
• that metal? M of Ca 40.08 g/mol
• 1 mol 6.022 x 1023 atoms
  
• 4.008 g x ------ x -------------
• 40.08 g 1 mol
• 6.022 x
  1022 Ca atoms

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• The density of Au is 19.32 g/cm3. What is the
  volume of a piece of gold that contains 2.6 x
  1024 atoms? If the piece of metal is a square
  with a thickness of 0.10 cm, what is the length
  (in cm) of one side of the square? AW 196.97
  g/mol
• 196.97 g
  Au
• 2.6 x 1024 atoms Au x ------------ 850 g Au
• 6.022 x 1023
  atoms
• 1 cm3
• 850 g Au x -------- 43 cm3 Au
• 19.32 g Au
• 
  
  side l
• 
  thickness (th)
• V th x A th x l2
• l SQRT (V/th) SQRT (43 cm3 / 0.10 cm) 21
  cm

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• What is the average mass of one germanium
  atom? M Ge 72.59 g/mol
• Here we have to divide the mass of a mole by
  the number of atoms in that mole.
• 1 mole Ge 72.59 g 6.02 x 1023 atoms
• 72.59 g Ge 1 mol Ge
  g Ge
• ------- x ------------- 1.205 x10-22 -----
• 1 mol Ge 6.022 x1023 atoms Ge
  1 atom Ge
• 0.0000000000000000000001205 g !!!!!!!

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Periodic Table()

• a listing of the elements arranged according to
  their chemical and physical properties
• elements are arranged according to similar
  properties.
• Groups or families contain elements with similar
  properties in vertical columns.
• periods are horizontal rows of elements. Every
  period has a number (row) from 1 through 7.
• () originally Mendeleev by atomic mass (1869),
  later Moseley by increasing atomic number (1913).

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Periodic Table
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Groups

• referred to by number or top element
• some have names
• The Representative Elements
• alkali metals - group 1A
• alkaline earth metals - group 2A
• noble gases - group 8A
• halogens - group 7A
• chalcogens - group 6A
• pnictogens - group 5A

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Alkali Metals

• Group 1A(1), the alkali metals, includes
  lithium, sodium, potassium, rubidium, cesium, and
  francium

ChemNow 2.17 Exercise
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Halogens

• Group 7A(17) the halogens, includes fluorine,
  chlorine, bromine, and iodine.

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Representative Elements
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Transition Elements
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Colors of solutions of Transition Metal Compounds
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Inner Transition Elements
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• rows periods
• gradual transition in properties from metallic to
  nonmetallic moving from left to right across a
  period

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Metals

• Malleable can be hammered or pressed into new
  shapes (coins, rings, etc.)
• Ductile can be pressed, beaten, or drawn into
  shape when cold (wires, such as Cu)
• solid at room temperature (except for Hg)
• luster
• photoelectric effect (e emission due to light)
• thermionic effect (e emission due to heat)
• readily lose electrons
• good thermal and electrical conductors

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Nonmetals

• solid, liquid, or gas
• brittle if solid (fracture)
• non-malleable, non-ductile
• thermal and electrical insulators
• do not exhibit photoelectric effect
• do not exhibit thermionic effect
• readily gain electrons

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Metalloids (Semimetals)

• properties intermediate to those of metals and
  nonmetals
• are located table around the solid ladder between
  metals and non-metals in periodic
• B, Si, Ge, As, Sb, Te, Po, At

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Noble gases

• Are the least reactive elements
• Are gases, none-abundant on Earth, but He is the
  second in the universe after hydrogen
• Neon in advertising signs
• Some lasers are made of He, Ar, Kr

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Learning Check

• Identify each of the following elements as
• 1) metal 2) nonmetal 3) metalloid
• A. sodium ____
• B. chlorine ____
• C. silicon ____
• D. iron ____
• E. carbon ____
• F. antimony ____

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Learning Check

• Match the elements to the description.
• A. Metals in Group 4A(14)
• 1) Sn, Pb 2) C, Si 3) C, Si, Ge,
  Sn
• B. Nonmetals in Group 5A(15)
• 1) As, Sb, Bi 2) N, P 3) N, P, As, Sb
• C. Metalloids in Group 4A(14)
• 1) C, Si, Ge, 2) Si, Ge 3) Si, Ge,
  Sn, Pb

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Learning Check

• The elements magnesium and calcium are in what
• group? 
• a. alkali metals b. alkaline earth
  metals
• c. halogens d. noble gases
• Which elements are nonmetals? 
• a. sodium and potassium
• b. magnesium and barium
• c. boron and aluminum d. carbon and
  bromine
• Identify the period number for the row that ends
  in
• argon. 
• a. Period 1 b. Period 2 c. Period 3
  d.Period 4

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Learning Check

• Which statement is characteristic of metals?A.
  They are shiny. B. They are poor conductors of
  electricity. C. They melt at high temperatures.
   
• a. statement A only b. statements A and B
  only
• c. statements A, B, and C
• d. statements A and C only
• Which statement is false?A. Potassium is an
  alkali metal. B. Strontium is an alkaline earth
  metal. C. Argon is a noble gas. D. Zinc in a
  halogen. 

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Learning Check

• What is the right order of increasing metallic
• character for the elements Rb, F, P, Ga?
• Rb lt F lt P lt Ga
• P lt F lt Rb lt Ga
• Galt Rb lt P lt F
• F lt P lt Ga lt Rb

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Learning Check

• How many atoms are in 1.50 mol Na?
• A.1.50 b. 9.03x1023 c. 3.00 d. 2.49x10-24
  e. 345
• 6.022?1023 atoms
• 1.50 mol ? ------------ 9.03 x 1023 atoms
• 1 mol
• How many moles of Ar in 5.22 x 1022 atoms of this
  
• noble gas? a. 11.5 b. 0.0867 c.
  1.15x1022
• d. 8.67x1023 e. 3.14 x 1046
• 1
  mol
• 5.22 x 1022 atoms ? ------------ 0.0867 mol
• 6.022?1023
  atoms

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Learning Check

• What is the mass (grams) of one atom of Na?
• a. 22.99 b. 0.04350 c. 3.818 x 10?23 b.
  2.619x1022
• 22.99 g
• 1 mol Na ----------- 3.818 x 10?23
  g/atom
• 6.022?1023 atoms