Introductory Chemistry, 2nd Edition Nivaldo Tro

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Introductory Chemistry, 2nd EditionNivaldo Tro
Chapter 4 Atoms and Elements
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Experiencing Atoms

• Atoms are very small they are building blocks of
  matter.
• Atom smallest particle of an element that
  retains its characteristics

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Daltons Atomic Theory

• Elements are composed of tiny indivisible
  particles called atoms
• All atoms of an element are identical atoms of
  different elements are different
• every carbon atom is identical to every other
  carbon atom
• they have the same chemical and physical
  properties
• but carbon atoms are different from sulfur atoms
• they have different chemical and physical
  properties

John Dalton (1766-1844)
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Daltons Atomic Theory

• Atoms combine in simple, whole-number ratios to
  form molecules of compounds
• each molecule of a compound contains the exact
  same types and numbers of atoms
• Law of Constant Composition or Definite
  Proportions
• Chemical Formulas

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Daltons Atomic Theory

• In chemical reactions, atoms are not broken or
  changed into other atoms.
• atoms are not created or destroyed, just
  rearranged
• total mass will remain the same
• Law of Conservation of Mass
• atoms of one element do not change into atoms of
  another element in a chemical reaction
• cannot turn Lead into Gold by a chemical reaction

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Daltons Atomic Theory

• Law of multiple proportions if two elements A
  and B combine to form more than one compound,
  masses of B which combine with mass of A, is a
  ratio of small whole numbers. Ex CO, (1.33 g
  O/1g C) CO2 (2.67 g O/g)
• The mass of O in CO2 is twice that in CO 2.67g O
  in CO2/1.33 g O in CO2 2.00
• Thus, when 2 elements combine to form 2 different
  compounds, they combine in different ratios or
  proportions
• CO, CO2 SO2, SO3

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Modern Evidence for Atoms
Atoms can be seen through a special instrument
called the scanning tunneling microscope (STM)
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Mass of Atoms

• Using compositions of compounds and assumed
  formulas, Dalton determined relative masses of
  atoms
• Dalton based his scale on H 1 amu
• we now base it on C-12 12 amu exactly
• unit atomic mass unit, amu

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The Atom is Divisible!

• Work done by J.J. Thomson and others proved that
  the atom had particles called electrons
• Thomson found that electrons are much smaller
  than atoms and carry a negative charge
• The mass of the electron is 1/1836th the mass of
  a hydrogen atom

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Rutherfords Experiment
Radioactive Sample
Lead Box
Fluorescent Screen
Gold Foil
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Conclusions from Rutherfords Experiment

• Atom mostly empty space
• because most particles went through
• Atom contains a dense particle that was small in
  volume compared to the atom but large in mass
• because of the few particles that bounced back
• This dense particle was positively charged
• because of the large deflections of some of the
  particles

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Rutherfords Interpretation the Nuclear Model

• Atom contains a tiny dense center called the
  nucleus
• The nucleus has essentially the entire mass of
  the atom
• the electrons weigh so little they give
  practically no mass to the atom
• The nucleus is positively charged
• the amount of positive charge balances the
  negative charge of the electrons
• The electrons move around in the empty space of
  the atom surrounding the nucleus

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The Modern Atom

• Atoms are composed of three particles - protons,
  neutrons and electrons
• The nucleus contains protons and neutrons
• The electrons move outside the nucleus
• Neutral atom has same protons and electrons.

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The Nuclear Atom
protons
Nucleus
neutrons


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Subatomic Particles
Charge? Location?
neutrons (n) protons (p) electrons (e)
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Subatomic Particles
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Subatomic Particles
Mass (amu)
1 1 ? 0 (1/1837)
neutron proton electron
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Elements

• Each element has a unique number of protons in
  its nucleus
• Number of protons in the nucleus of an atom is
  called the atomic number
• the elements are arranged on the Periodic Table
  in order of their atomic numbers
• Each element has a unique name and symbol
• symbol either one or two letters
• one capital letter or one capital letter one
  lower case

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How many?

• protons depends on element
• neutrons variable for each element
• electrons same as protons

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atomic number -

• The number of protons in one atom each element
  has a different atomic number
• The number on top of the element symbol in the
  periodic table

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The Periodic Table of Elements
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Review

• What is the atomic number of boron, B?
• What is the atomic mass of silicon, Si?
• How many protons does a chlorine atom have?
• How many electrons does a neutral neon atom have?
  
• Will an atom with 6 protons, 6 neutrons and 6
  electrons be electrically neutral?
• Will an atom with 27 protons, 32 neutrons and 27
  electrons be electrically neutral?
• Will a Na atom with 10 electrons be electrically
  neutral?

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Review

• What is the atomic number of boron, B? 5
• What is the atomic mass of silicon, Si? 28.09
  amu
• How many protons does a chlorine atom have? 17
• How many electrons does a neutral neon atom have?
  10
• Will an atom with 6 protons, 6 neutrons and 6
  electrons be electrically neutral? Yes
• Will an atom with 27 protons, 32 neutrons and 27
  electrons be electrically neutral? Yes
• Will a Na atom with 10 electrons be electrically
  neutral? No

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Three Types of Elements
Metal
Metalloid
Nonmetal
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Metals

• Solids at room temperature, except Hg
• Shiny
• Conduct heat, electricity
• Malleable can be shaped
• Ductile drawn or pulled into wires
• Lose electrons and form cations ( charge) in
  reactions
• About 75 of the elements are metals

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Nonmetals

• Found in all 3 states
• Poor conductors of heat electricity
• Solids are brittle
• Gain electrons in reactions to become anions (-
  charge)
• Only a few on the right of periodic table

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Metalloids

• Show some properties of metals and some of
  nonmetals
• Also known as semiconductors

Properties of Silicon shiny conducts
electricity does not conduct heat well brittle
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The Modern Periodic Table

• Elements with similar chemical and physical
  properties are in same column
• Columns are called Groups or Families
• designated by a number and letter at top
• Rows are called Periods
• Each period shows the pattern of properties
  repeated in the next period

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The Modern Periodic Table

• Main Group Representative Elements A groups
• Transition Elements B groups
• all metals
• Bottom rows Inner Transition Elements Rare
  Earth Elements
• metals
• really belong in Period 6 7

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Halogens
Lanthanides
Actinides
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Important Groups - Hydrogen

• nonmetal
• colorless, diatomic gas
• very low melting point density
• reacts with nonmetals to form molecular compounds
• HCl is acidic gas
• H2O is a liquid
• reacts with metals to form hydrides
• metal hydrides react with water to form H2
• HX dissolves in water to form acids

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Important Groups IA, Alkali Metals

• hydrogen usually placed here, though it doesnt
  belong
• soft, low melting points,low density
• very reactive, never find uncombined in nature
• tend to form water soluble compounds
• react with water to form basic (alkaline)
  solutions and H2 releasing a lot of heat

lithium
sodium
potassium
rubidium
cesium
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Important Groups IIA, Alkali Earth Metals

• harder, higher melting, and denser than alkali
  metals
• reactive, but less than corresponding alkali
  metal
• form stable, insoluble oxides from which they are
  normally extracted
• oxides are basic alkaline earth

beryllium
magnesium
calcium
strontium
barium
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Important Groups VIIA, Halogens

• nonmetals
• F2 Cl2 gases Br2 liquid I2 solid
• all diatomic
• very reactive
• react with metals to form ionic compounds
• HX all strong acids except HF

fluorine
chlorine
bromine
iodine
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Important Groups VIIIA, Noble Gases

• all gases at room temperature,
• very low melting and boiling points
• very unreactive, practically inert
• very hard to remove electron from or give an
  electron to

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Charged Atoms Ions

• Number of protons (atomic ) identifies the
  element!
• all sodium atoms have 11 protons in the nucleus
• In chemical change, number of protons in
  nucleus of atom doesnt change!
• Atoms can lose or gain electrons becoming
  electrically charged, these are called ions

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Ions

• Atoms acquire a charge by gaining or losing
  electrons
• not protons!!
• Ion Charge protons electrons
• ions with a charge are called cations
• more protons than electrons
• form by losing electrons
• ions with a charge are called anions
• more electrons than protons
• form by gaining electrons

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Atomic Structures of Ions

• Metals form cations
• For each positive charge the ion has 1 less
  electron than the neutral atom
• Na atom 11 p and 11 e-, Na ion 11 p and 10
  e-
• Ca atom 20 p and 20 e-, Ca2 ion 20 p and
  18 e-
• Cations are named the same as the metal
• sodium Na ? Na 1e- sodium ion
• calcium Ca ? Ca2 2e- calcium ion
• The charge on a cation can be determined from the
  Group number on the Periodic Table
• Group 1A ? 1, Group 2A ? 2, (Al, Ga, In) ? 3

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Atomic Structures of Ions

• Nonmetals form anions
• For each negative charge the ion has 1 more
  electron than the neutral atom
• F 9 e-, F- 10 e-
• P 15 e-, P3- 18 e-
• Anions are named by changing the ending of the
  name to -ide
• fluorine F 1e- ? F- fluoride ion
• oxygen O 2e- ? O-2 oxide ion
• Charge on an anion can be determined by
  subtracting 8 from the Group number on the
  Periodic Table
• Group 7A ? 7- 8 -1 Group 6A ? 6 8 -2

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Example 4.5 Determining the Number of Protons
and Electrons in an Ion
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• Example
• Find the number of protons and electrons in the
  Ca2 ion.

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ExampleFind the number of protons and electrons
in the Ca2 ion

• Write down the given quantity and its units.
• Given Ca2

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ExampleFind the number of protons and electrons
in the Ca2 ion

• Information
• Given Ca2

• Write down the quantity to find and/or its units.
  
• Find p and e

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ExampleFind the number of protons and electrons
in the Ca2 ion

• Information
• Given Ca2
• Find p and e

• Design a Solution Map.

ion symbol
and e
Ion charge p - e
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ExampleFind the number of protons and electrons
in the Ca2 ion

• Information
• Given Ca2
• Find p and e
• Solution Map ion symbol ? element ? atomic
  number ? p ? e

• Apply the Solution Map.
• Determine the Name of the Element

Ca calcium
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ExampleFind the number of protons and electrons
in the Ca2 ion

• Information
• Given Ca2 calcium
• Find p and e
• Solution Map ion symbol ? element ? atomic
  number ? p ? e

• Apply the Solution Map.
• Determine the Atomic Number of the Element

Ca calcium Atomic Number 20
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ExampleFind the number of protons and electrons
in the Ca2 ion

• Information
• Given Ca2 calcium, Z 20
• Find p and e
• Solution Map ion symbol ? element ? atomic
  number ? p ? e

• Apply the Solution Map.
• Determine the Number of Protons in an Atom of the
  Element

Ca calcium Atomic Number 20 p atomic
number 20
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ExampleFind the number of protons and electrons
in the Ca2 ion

• Information
• Given Ca2 calcium, Z 20
• Find p 20 and e
• Solution Map ion symbol ? element ? atomic
  number ? p ? e

• Apply the Solution Map.
• Determine the Number of Electrons in an Ion of
  the Element

Ion Charge p - e 2 20 - e -18 - e 18
e
Ca calcium Atomic Number 20 p atomic
number 20
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Atomic Structures of Ions
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Atomic Structures of Ions
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Ion Charge the Periodic Table

• Charge on an ion can often be determined from an
  elements position on the Periodic Table
• Metals are always positive ions, nonmetals are
  negative ions
• For many main group metals, the charge the
  group number
• For nonmetals, the charge the group number - 8

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Charges of Main Group Ions
IA
VIA
IIA
IIIA
VIIA
VA
Li1
Be2
O-2
F-1
N-3
Mg2
Na1
S-2
Cl-1
P-3
Al3
K1
Ca2
Se-2
Br-1
As-3
Ga3
Rb1
Sr2
Te-2
I-1
In3
Cs1
Ba2
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Isotopes

• Isotopes atoms of an element that have same
  of protons but different of neutrons
• Isotopes of an element have different masses
• isotopes are identified by their
• mass numbers protons neutrons
• All isotopes of an element are chemically
  identical
• undergo the exact same chemical reactions

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Isotopes

• Atomic Number
• Number of protons
• Z (symbol)
• Mass Number
• Protons Neutrons
• Whole number
• A (symbol)
• Abundance relative amount found in a sample

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Neon
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Isotope Symbols

• Cl-35 makes up about 75 of chlorine atoms in
  nature, and Cl-37 makes up the remaining 25
• Average atomic mass of Cl 35.45 amu
• Cl-35 has a mass number 35, 17 protons and 18
  neutrons (35 - 17)

or Cl-35
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Example 4.8 Determining the Number of Protons
and Neutrons fromIsotope Symbols
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• Example
• How many protons and neutrons in the chromium
  isotope

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ExampleHow many protons and neutrons in the
chromium isotope

• Write down the given quantity and its units.
• Given

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ExampleHow many protons and neutrons in the
chromium isotope

• Information
• Given

• Write down the quantity to find and/or its units.
  
• Find p and n

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ExampleHow many protons and neutrons in the
chromium isotope

• Information
• Given
• Find p and n

• Design a Solution Map.

ion symbol
Mass p n
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ExampleHow many protons and neutrons in the
chromium isotope

• Information
• Given
• Find p and n
• Solution Map ion symbol ? element ? atomic
  number ? p ? n

• Apply the Solution Map.
• Determine the Name of the Element

Cr chromium
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ExampleHow many protons and neutrons in the
chromium isotope

• Information
• Given calcium
• Find p and n
• Solution Map ion symbol ? element ? atomic
  number ? p ? n

• Apply the Solution Map.
• Determine the Atomic Number of the Element

Cr chromium Atomic Number 24
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ExampleHow many protons and neutrons in the
chromium isotope

• Information
• Given calcium
• Find p and n
• Solution Map ion symbol ? element ? atomic
  number ? p ? n

• Apply the Solution Map.
• Determine the Number of Protons in an Atom of the
  Element

Cr chromium Atomic Number 24 p atomic
number 24
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ExampleHow many protons and neutrons in the
chromium isotope

• Information
• Given calcium
• Find p and n
• Solution Map ion symbol ? element ? atomic
  number ? p ? n

• Apply the Solution Map.
• Determine the Number of Neutrons in an Atom of
  the Element

Cr chromium Atomic Number 24 p atomic
number 24
Mass Number p n 52 24 n 28 n
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Practice - Complete the following table
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Practice - Complete the following table
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Mass Number is Not the Sameas Atomic Mass

• The atomic mass is an experimental number
  determined from all naturally occurring isotopes
• The mass number refers to the number of protons
  neutrons in one isotope
• natural or man-made