Title: Chapter 3: Atoms
1Chapter 3 Atoms the Periodic Table
2These are uranium atoms. What do they look
like? What actually are you seeing?
3Section 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
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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
6The atoms nucleus contains protons and neutrons.
The high energy electrons move in the space
around the nucleus called the electron cloud.
7Atomic 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.
8Atomic 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.
12The 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.
13Imagine the blades of a moving fan.
14Little 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?
16Valence 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
19Electron 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.
21Models 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
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23Models 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
24THOMPSONS MODEL
25Models 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.
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27Models of Atoms
- 1911-Rutherford Model
- Atom is mostly empty space.
- Electrons orbit randomly around a small,
positively charged nucleus.
28RUTHERFORDS MODEL
29Rutherfords Experiment - showed that particles
were deflected by something in atoms. He deduced
that this was a positively charged nucleus.
30Models 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
31BOHRS MODEL
32Models 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.
33Models 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
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35Section 2 Organizing the Elements
36The 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.
37Modern 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
38This 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.)
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40Reading the Periodic Table
- Each square of the table usually includes the
elements atomic number, chemical symbol, name,
and atomic mass.
41Elements Name
Atomic Number
Elements Symbol
Atomic Mass
42An elements properties can be predicted from its
location in the periodic table!
43Organization 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
44Group 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
47Periods
48Why 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
50Section 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
53Chemical 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
55Alloys
- 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
57Metals 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.
58Alkali 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)
60Alkaline 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
62Transition 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
64Metals 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
65Lanthanides 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)
67Section 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
69Chemical 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?
70Compounds 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?
72How 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)
74Diatomic molecule of H2 (Hydrogen)
75Families 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)
84Metalloids
- 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
87Section 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