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Chapter 3: Atoms

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Title: Chapter 3: Atoms


1
Chapter 3 Atoms the Periodic Table
2
These are uranium atoms. What do they look
like? What actually are you seeing?
3
Section 1 Inside an Atom
  • Structure of an Atom
  • An atom consists of a nucleus surrounded by one
    or more electrons.
  • The nucleus is the tiny, central core of an atom

4
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5
  • An atom has 3 types of particles
  • (subatomic particles)
  • Protons -- have a positive electric charge are
    located in the nucleus
  • Neutrons -- have a neutral electric charge are
    located in the nucleus
  • Electrons -- have a negative electric charge
    are located outside of the nucleus

6
The atoms nucleus contains protons and neutrons.
The high energy electrons move in the space
around the nucleus called the electron cloud.
7
Atomic Number the number of protons in a nucleus
  • Is a unique property that identifies the element
  • Ex Every Carbon atom has 6 protons
  • In an atom, the of protons the of electrons
    are equal, making the atom neutral.

8
Atomic Mass the average mass of one atom of an
element
  • Since atoms are so small, they are measured in
    atomic mass units (amu).
  • The mass of a proton or a neutron is about one
    amu.
  • Electrons are much smaller.

9
  • It takes almost 2000 electrons to equal one amu!
  • Therefore, most of an atoms mass is in the
    nucleus of an atom.
  • Ex An atom that has 6 protons, 6 neutrons, and 6
    electrons has a mass of about 12 amus

10
  • The number of protons in an element does not
    change
  • the number of neutrons can change. (Isotopes of
    an atom)
  • Ex Carbon atoms always have 6 protons. But
    they may have 5,6,7,or 8 neutrons. (Isotopes of
    carbon)
  • This means that the amu will vary.

11
  • Since neutrons dont play a role in chemical
    reactions, the chemical properties of each
    element are the same despite having different
    masses.

12
The Role of Electrons
  • Electrons move around the nucleus so fast that it
    is impossible to know exactly where any electron
    is at a particular time!
  • Its like a spherical cloud of negatively charged
    electrons.

13
Imagine the blades of a moving fan.
14
Little Particles, Big Spacesvideo
  • The space in which electrons move is HUGE!!!
  • Ex Imagine standing at the pitchers mound in a
    baseball stadium. If the nucleus were the size
    of a pencil eraser, the electrons could be in the
    outfield or the top row of seats!

15
  • So, what composes the majority of an atoms mass?
  • What composes the majority of an atoms volume?

16
Valence Electrons
  • Electrons in an atom are not all the same
    distance away from the nucleus.
  • Valence electrons are those that are the farthest
    away.

17
  • A chemical bond forms between 2 atoms when
    valence electrons move between them.
  • Valence electrons may be transferred from one
    atom to another, or they may be shared between
    atoms.

18
  • The number of valence electrons can vary from 1
    to 8.
  • Each element has a typical of valance
    electrons.
  • Ex Oxygen has 6, Carbon has 4, Hydrogen has 1

19
Electron Dot Diagrams
  • Used to represent valence electrons.
  • A symbol for an element is surrounded by dots.
    Each dot stands for one valence electron.

20
  • When atoms have 8 or 0 valence electrons, the
    atom becomes more stable- or less reactive than
    they were before.

21
Models of Atoms
  • 1808- Dalton Model
  • each element is made of small atoms different
    elements have atoms of different masses
  • atoms similar to tiny, solid balls

22
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23
Models of Atoms
  • 1897-Thomson Model
  • Atom is a positively charged sphere with
    electrons embedded in it.
  • Similar to a muffin w/ berries scattered through
    it

24
THOMPSONS MODEL
25
Models of Atoms
  • 1904- Nagaoka Model
  • Atom had a large sphere in the center with a
    positive charge.
  • Electrons revolved around the sphere like
    planets revolve around the sun.

26
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27
Models of Atoms
  • 1911-Rutherford Model
  • Atom is mostly empty space.
  • Electrons orbit randomly around a small,
    positively charged nucleus.

28
RUTHERFORDS MODEL
29
Rutherfords Experiment - showed that particles
were deflected by something in atoms. He deduced
that this was a positively charged nucleus.
30
Models of Atoms
  • 1913-Bohr Model
  • Electrons move in specific layers, or shells
  • Atoms absorb or give off energy when the
    electrons move from one shell to another

31
BOHRS MODEL
32
Models of Atoms
  • 1932-Chadwick Model
  • Discovered the neutron.
  • The existence of the neutron explained why atoms
    were heavier than the total mass of their protons
    and electrons.

33
Models of Atoms
  • 1920s to Present- Modern Model
  • Electrons form a negatively charged cloud around
    the nucleus.
  • Its impossible to determine the exact location
    of an electron

34
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35
Section 2 Organizing the Elements
36
The Periodic Table
  • Mendeleev patterns appeared when the elements
    were arranged in order of increasing atomic mass.
  • Sometimes this method didnt work, so he would
    put the elements in a best fit location.

37
Modern Periodic Table
  • Based on atomic number (discovered in the 1900s)
    rather than atomic mass
  • the properties of the elements repeat in each
    period (row) of the table

38
This is Henry Mosley, a British scientist. He
created the modern periodic table of elements by
placing the elements in order of their atomic
number instead of mass. (He was only 27 years
old when he was killed in WWI.)
39
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40
Reading the Periodic Table
  • Each square of the table usually includes the
    elements atomic number, chemical symbol, name,
    and atomic mass.

41
Elements Name
Atomic Number
Elements Symbol
Atomic Mass
42
An elements properties can be predicted from its
location in the periodic table!
43
Organization of the Periodic Table
  • Main body of table has 18 vertical columns 7
    horizontal rows
  • The elements in a column are called a group
  • Groups are also known as families

44
Group Numbers
45
  • The elements in each group, or family, have
    similar characteristics.
  • Ex elements in group 1A are all metals that
    react violently with water. Elements in group 18
    rarely react at all

46
  • Each horizontal row across the table is called a
    period
  • Elements in a period have very different
    properties
  • As you move across a period from left to right,
    those properties change according to a pattern

47
Periods
48
Why the Periodic Table Works
  • Because it is based on the structure of atoms,
    especially the valence electrons.
  • Elements in a family all have the same number of
    valence electrons
  • This is a reason why the elements in a particular
    group have similar properties

49
  • As you move from left to right across a period,
    the atomic number increases by one
  • This means that an element has one more valence
    electron than the element to its left

50
Section 3 Metals
51
  • Physical properties of metals
  • hardness,
  • shininess,
  • malleability (can be pounded or rolled into
    shapes) ,
  • ductility (can be pulled out or drawn into wires)

52
  • Most metals are good conductors because they
    transmit heat and electricity easily
  • Several metals are magnetic (attracted to
    magnets)--iron (Fe), cobalt (Co), and nickel (Ni)
  • Most metals are solids at room temperature ( they
    have a high melting point)
  • exception is mercury(Hg)--liquid at room
    temperature

53
Chemical Properties of Metals
  • Metals have a wide range of chemical properties
  • Some are very reactive sodium (Na), potassium
    (K)
  • Some are unreactive gold (Au) and chromium (Cr)

54
  • Some metals are in the middle. These metals
    react slowly with oxygen in the air, forming
    metal oxides
  • Ex Iron left unprotected will slowly rust (turn
    a reddish brown)
  • Process of reaction and wearing away Corrosion

55
Alloys
  • Alloy a mixture of metal (Remember a mixture
    consists of 2 or more substances mixed together
    but not chemically changed)

56
  • Some common alloys
  • Copper Tin Bronze
  • Copper Zinc Brass
  • Iron Carbon Chromium Vanadium Stainless
    Steel
  • Gold Silver Copper a little Zinc Yellow
    Gold
  • Gold Nickel Copper Zinc White Gold

57
Metals in the Periodic Table
  • The metals in a group, or family, have similar
    properties, and these family properties change
    gradually as you move across the table.

58
Alkali Metals
  • Metals in Group 1- from Li to Fr
  • These are the most reactive metals since they
    only have 1 valence electron
  • In nature, these are never found as
    elements--exist only as compounds

59
  • As elements, they are very soft shiny
  • Most important alkali metals are
  • Sodium (Na)
  • Potassium (K)

60
Alkaline Earth Metals
  • Group 2 alkaline earth metals
  • Not as reactive as Group 1 but they are more
    reactive than most metals
  • Never found uncombined in nature
  • They have 2 valence electrons

61
  • Most common alkaline earth metals
  • magnesium (Mg) -- used to be in flash bulbs
    because of the very bright light
  • calcium (Ca) --important in bones and teeth

62
Transition Metals
  • Elements in group 3 - 12 are the transition
    metals
  • These metals form a bridge between the reactive
    metals on the left to the less reactive metals on
    the right

63
  • Example of transition metals
  • iron, copper, nickel, silver, and gold
  • Most are hard and shiny
  • All are good conductors of electricity
  • Are fairly stable, reacting slowly or not at all
    with air and water

64
Metals in Mixed Groups
  • Groups 13 - 16 include metals, nonmetals, and
    metalloids
  • Not as reactive as the metals in groups 3 - 12
  • Ex aluminum, tin, and lead

65
Lanthanides Actinides
  • At the bottom of the periodic table,
  • the top row Lanthanides
  • bottom row Actinides
  • These elements are called the rare earth elements
    they fit in Periods 6 7

66
  • Lanthanides soft, malleable, shiny metals w/
    high conductivity
  • Actinides
  • only thorium and uranium exist on Earth in
    significant amounts
  • All the elements after uranium were created
    artificially in the lab
  • the nuclei of these elements are very unstable
    (many last for only a fraction of a second after
    they are made)

67
Section 4 Nonmetals Metalloids
  • Nonmetals elements that lack most of the
    properties of metals
  • The 17 nonmetals are to the right of the zig zag
    on the periodic table

68
  • In general, nonmetal physical properties are
    opposites of metal properties. Most nonmetals
    are
  • Dull,
  • Solid nonmetals are brittle (not malleable or
    ductile)
  • Poor Conductors of heat electricicity

69
Chemical Properties of Nonmetals
  • Most nonmetals form compounds easily EXCEPT those
    from Group 18 (Noble Gases)
  • Reason group 18 doesnt gain, lose, or share
    electrons with other elements. Why?

70
Compounds of Nonmetals
  • When nonmetals and metals react, valence
    electrons move from the metal atoms to the
    nonmetal atoms. (See pg 99)
  • Table Salt Na (metal) Cl (nonmetal)

71
  • How many valence electrons does Na (sodium) have?
  • How many valence electrons does Cl (chlorine)
    have?
  • Are valence electrons shared or transferred to
    make NaCl?
  • Which element transferred the valence electron in
    order to make table salt?

72
How many valence electrons does Hydrogen have?
Chlorine? Are the valence electrons transferred
or shared? by whom?
73
  • Nonmetals can also form compounds with other
    nonmetals
  • The atoms share electrons and become bonded
    together into molecules.
  • Diatomic moleculesmolecules have only 2 atoms
  • Ex Oxygen (O2), Nitrogen (N2), and Hydrogen (H2)

74
Diatomic molecule of H2 (Hydrogen)
75
Families of Nonmetals
  • Carbon Family (Group 14)
  • Each element has 4 valence e-
  • Carbon nonmetal
  • Silicon Germanium metalloids
  • Tin Lead metals

76
  • Nitrogen Family (Group 15)
  • Each element has 5 valence e-
  • Nonmetals
  • N Nitrogen gas is 80 of the air
  • P always found in compounds
  • As Sb metalloids
  • Bi metal

77
  • Oxygen Family (Group 16)
  • Each element has 6 valence e-
  • Usually gain/share 2 e- when they react
  • Nonmetals
  • Oxygen very reactive can combine with most
    elements most abundant element in Earths crust
    2nd in the atmosphere

78
  • Sulfur strong, unpleasant odor in rubber bands,
    car tires, medicine
  • Selenium
  • Metalloid Tellurium
  • Metal Plonium

79
  • Halogen Family (Group 17)
  • All except Astatine are nonmetals
  • All have 7 valence e-
  • Typically gain/share 1 valence e-
  • All are very reactive most are dangerous to
    people
  • Fluorine most reactive nonmetal found in
    nonstick cookware toothpaste

80
  • Chlorine used in table salt (NaCl), and used to
    melt snow (CaCl)
  • Bromine when with Silver (AgBr) used in
    photographic film

81
  • Noble Gases (Group 18)
  • Do not usually form compounds since some dont
    gain/lose/share their valence e-
  • All exist in the atmosphere but in small amounts
  • Can be found in glowing electric lights (neon
    lights) but are filled with Ar, Xe, or other
    noble gases

82
  • Hydrogen
  • Simplest element (usually 1 proton 1 electron)
  • Since chemical properties are so different from
    other elements, it cant really be put into a
    family
  • 90 of the atoms in universe
  • 1 of the mass of Earths crust, oceans, and
    atmosphere

83
  • Hydrogen usually found on Earth as a compound
    (combined with oxygen in water)

84
Metalloids
  • 7 of them on the border between metals and
    nonmetals
  • Have similar properties as the metals and
    nonmetals

85
  • Silicon (Si) is the most common
  • when combined with Oxygen, it can form sand,
    glass, and cement
  • Most useful property is their varying ability to
    conduct electricity
  • it would depend on temperature, exposure to
    light, or impurities

86
  • The varying ability to conduct electricity is why
    these elements are used to make semiconductors
  • Semiconductorssubstances that under some
    conditions can carry electricity, while under
    other conditions cannot carry electricity
  • Semiconductors are used to make computer chips,
    transistors, lasers

87
Section 5 Elements from Stardust
  • Atomic Nuclei Combine
  • Sun is made mostly of H which exists at high
    temp(15 million degrees Celsius) pressure (This
    state of matter plasma)
  • Plasma atoms are stripped of their electrons,
    the nuclei are packed close together

88
  • Usually positively charged nuclei repel each
    othen stars (the plasma state)nuclei are close
    enough and moving fast enough to collide with one
    another
  • In Nuclear Fusion, atomic nuclei combine to form
    a larger nucleus, releasing huge amounts of energy

89
  • Inside stars, nuclear fusion combines smaller
    nuclei into larger nuclei, thus creating heavier
    elements
  • Think of stars as element factories

90
  • Elements from the Sun
  • When 2 hydrogen nuclei with neutrons join
    together, they produce a helium nucleus.
    Releasing a lot of energy
  • This reaction is a major source of the suns
    energy
  • Estimate that the sun has enough hydrogen to last
    another 5 billion years

91
  • As helium builds up, the volume temp of suns
    core changes. This allows different nuclear
    fusion reactions to occur
  • Stars the size of the sun do not contain enough
    energy to produce elements heavier than oxygen

92
  • A very massive star can explode (a supernova)
    providing enough energy for nuclear fusion
    reactions that create the heaviest elements.
  • Theory Matter in the sun planets around it
    originally came from a gigantic supernova that
    occurred billions of years ago
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