Ch. 3: Atoms

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Ch. 3 Atoms Elements

• Chem. 20
• El Camino College

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Matter
One substance from the periodic table. Ex. Na,
He, H2, Br2
More than one substance from the periodic table,
bonded together. Ex. H2O, NaCl, C6H12O6
Ex. Sugar soln., Windex
Ex. Beach sand, wood
Fig. 2-18, p. 32
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The Periodic Table

• Groups are vertical. Ill use old gp s 1-8 for
  the representative elements
• Periods are horizontal
• The stair-step line separates the metals from the
  nonmetals
• Elements touching the stair-step line (except for
  Al) are called metalloids or semi-metals. They
  have properties of metals and nonmetals.

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The Periodic Table
nonmetals.
metals
transition elements
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Nuclear Model of the Atom

• Atoms contain a tiny, dense nucleus
• All the positive charges and nearly all the mass
  are concentrated in the nucleus
• The nucleus is surrounded by a large volume of
  empty space (with some electrons)
• The minus charges of the e-s cancel the plus
  charges of the protons.

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Proof of the Nucleus
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Subatomic Particles

• Subatomic particles make up the atom
• Electrons (e-) have a -1 charge
• The mass of an electron 0 amu
• Protons (p) have a 1 charge
• The mass of a proton 1 amu
• Neutrons (n) are neutral
• The mass of a neutron 1 amu

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Atomic Number

• Note--The number of protons determines the
  element.
• Atomic Number p
• For uncharged atoms, p e-s

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Mass Number

• Mass Number p n
• Isotope Atoms of the same element that have a
  different n

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Nuclear Symbol
mass pn
element symbol
atomic p
138
56
82
138 - 56 82 neutrons
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Atomic Models

• The Bohr model of the atom is the one were
  familiar with e-s orbit a dense nucleus
• In the Quantum model, e-s are displayed in a
  probability map e-s have a high probability of
  existing where the map shows highest density.
• The Quantum model is the result of complex
  calculus.

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Fig. 10-6, p. 269
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Sublevels

• e-s exist on different sublevels
• Sublevels are indicated by the letters s, p, d,
  and f
• Different sublevels have different shapes.

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Principle Energy Levels (n)

• The period determines the highest principle
  energy level for an element
• For example, lithium is in period 2
• The highest principle energy level for lithium is
  n2.

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Valence Electrons

• Valence e-s are the e-s in the outermost energy
  level
• For main group elements,
  gp gives the valence e-s.

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Valence Electrons

• The e-s in the outer most shell are called the
  valence e-s.

Gp 1 ? 1 e- Gp 2 ? 2 e- Gp 13 ? 3 e- Gp 14 ? 4 e-
Gp 15 ? 5 e- Gp 16 ? 6 e- Gp 17 ? 7 e- Gp 18 ? 8
e-
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Lewis Dot Structures

• Valence e-s from Gp s (1, 2, 13-18)
• H has 1 valence e-, He has 2 valence e-s
• Show dots around the element symbol

Ex. Draw Lewis structures for H, Be, Ne, C, N, S
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Fig. 10-14, p. 284
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Periodic Table Trends

• Atomic Size (Atomic Radius) inc going down the
  periodic table and inc from right to left

Going down the periodic table, principle energy
levels (shells) are added. From left to right,
more charges (protons) in the nucleus pull
the e- shells closer.
Ex. Which has a larger atomic radius? Br or
Cl O or B Li or Be
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Periodic Table Trends

• First Ionization Energy--energy required to
  remove one e- (high ionization energy means its
  hard to remove an e-).

Metals lose e-s much more easily than nonmetals
Metals can form positive ions. The more
metallic the element, the easier it is to lose
an e-. Note, its very difficult to remove an e-
from a Noble Gas.
Ex. Which has a higher ionization energy? Br or
Cl O or B Li or Be
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Examples

• Element, compound, homogeneous mixture, or
  heterogeneous mixture?
• striped candy cane
• bromine
• diamond
• cat
• ethanol (C2H5OH)
• bubbling champagne
• iron
• 14K gold
• twinkie
• motor oil

heterogeneous mixture
element
element
heterogeneous mixture
compound
heterogeneous mixture
element
homogeneous mixture
heterogeneous mixture
homogeneous mixture
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Fig. 2-14, p. 28
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Fig. 2-9, p. 25
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p. 24
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p. 39
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Examples

• Pure or a mixture?
• oxygen, calcium chloride, grass, diet soda
• Element or compound?
• copper, lithium oxide, neon, sugar
• Homogeneous or heterogeneous?
• white wine, wood, chunky peanut butter

pure
pure
mixture
mixture
element
element
compound
compound
heterogeneous
heterogeneous
homogeneous
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The Periodic Table

• Elements in a group have similar properties
• Some important groups have names
• Group 1 Alkali Metals
• Group 2 Alkaline Earth Metals
• Group 17 Halogens
• Group 18 Noble Gases
• Note--H may appear twice on the table due to
  special reactivity. It is not a metal or a
  halogen.

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Metals vs. Nonmetals

• Metals
• Lose electrons easily to form cations
• Low ionization energies
• Form compounds with nonmetals, but not with other
  metals
• Conduct heat and electricity
• Can be made into sheets (malleable) or wires
  (ductile)

• Nonmetals
• Gain electrons easily to form anions
• High ionization energies
• Form compounds with nonmetals or metals
• Low conductivity
• Brittle, not malleable or ductile.

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Daltons Atomic Theory (1808)(parts have been
disproved)

• Elements are made of tiny particles called atoms
• Atoms cannot be divided, created, or destroyed
• All atoms of an element are identical
• Atoms of one element are different from atoms of
  any other element
• Atoms of different elements combine in
  whole-number ratios to form compounds.

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Examples

• How many protons in potassium?
• How many electrons in potassium?
• How many protons in mercury?
• How many electrons in mercury?

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80
80
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Fill in the Missing Info
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Review of Important Group Names

• Group 1 Alkali Metals
• 1 valence e-
• Group 2 Alkaline Earth Metals
• 2 valence e-s
• Group 17 Halogens
• They have 7 valence e-s
• Group 18 Noble Gases
• They are extremely unreactive
• They have 8 valence e-s (except He has 2 valence
  e-s).

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Fig. 10-12, p. 281