Warm Up 10/19/12
How long have people been interested in
understanding matter and its structure?
A.
B.
C.
D.
Thousands of years
Hundreds of years
A few years
Never
What is an atom?
 The smallest particle of an element.
 Atoms are so small that we cannot even see them with
a microscope.
 How do scientists know what they look like or how
they are made?
Democritus
Aristotle
http://www.youtube.com/watch?v=lY-Thmrt1Ts
Ancient Philosophy
 Who: Aristotle, Democritus
 When: More than 2000 years ago
 Where: Greece
 What:
 Aristotle believed in 4 elements: Earth, Air, Fire, and Water.
 Democritus believed that matter was made of small
particles that could not be divided. He named them “atoms”
meaning uncut or indivisible.
 Why: Aristotle and Democritus used observation and
inference to explain the existence of everything.
Alchemists
 Who: European Scientists
 When: 800 – 900 years ago
 Where: Europe
 What: Their work developed into
what is now modern chemistry.
 Why: Trying to change ordinary
materials into gold.
Alchemic Symbols
Becquerel and Curie
 Henri Becquerel—(1896)-- While studying the effect of
x-rays on photographic film, he discovered some
chemicals spontaneously decompose and give off very
penetrating rays.
 Marie Curie—(1898)--Studied uranium and thorium and
called their spontaneous decay process "radioactivity".
She and her husband Pierre also discovered the
radioactive elements polonium and radium.
 Lavoisier— elements combine to form compounds.
 Proust—Law of Definite Proportions
 The mass of elements of reactants equals the mass of
elements of products.
Particle Theory
 Who: John Dalton
 When: 1808
 Where: England
 What: Described atoms as tiny particles
that could not be divided. Thought each
element was made of its own kind of atom.
 Why: Building on the ideas of Democritus
in ancient Greece.
John Dalton
The Atomic Theory
 All elements are composed of atoms.
 All atoms of the same element are the same, but
different from other elements. They have same size,
mass and properties.
 Compounds contain atoms of more than one element,
combined in whole number ratios.
 Compounds form when atoms join, separate, or
rearrange.
John Dalton
Discovery of Electrons
 Who: J. J. Thompson
 When: 1897
 Where: England
 What: Thompson discovered that
electrons were smaller particles of an
atom and were negatively charged.
 Why: Thompson knew atoms were
neutrally charged, but couldn’t find the
positive particle.
J. J. Thomson
 First to show atoms are made of subatomic particles.
 Plum pudding model or chocolate chip ice cream
model. Pudding or ice cream is positive charged mass
o f matter and plums or chocolate chips are the
negative charges evenly scattered throughout the
atom.
 Used an electric current and the cathode ray tube to
learn more about atoms.
J. J. Thompson
Atomic Structure I
 Who: Ernest Rutherford
 When: 1911
 Where: England
 What: Conducted an experiment to isolate the
positive particles in an atom. Decided that the
atoms were mostly empty space, but had a dense
central core.
 Why: He knew that atoms had positive and negative
particles, but could not decide how they were
arranged.
Rutherford
 The atom is mostly empty space.
 All of the positive charge is located in the center of the
atom in the nucleus.
 Electrons move randomly in the space around the
nucleus.
 Used the gold foil experiment.
 http://www.mhhe.com/physsci/chemistry/essentialch
emistry/flash/ruther14.swf
Ernest Rutherford
Chadwick
 Protons and neutrons in nucleus.
 Protons –positive
 Neutrons-neutral
 Electrons-negative
 Proton mass = neutron mass; electrons much smaller
Atomic Structure II
 Who: Niels Bohr
 When: 1913
 Where: England
 What: Proposed that electrons traveled in fixed paths
around the nucleus. Scientists still use the Bohr model to
show the number of electrons in each orbit around the
nucleus. (energy levels)
 Why: Bohr was trying to show why the negative electrons
were not sucked into the nucleus of the atom.
Niels Bohr
Modern Model/Wave Model
Shrodinger—Electron Cloud Model
 Uses mathematical model to describe the certainty of
finding an electron at a certain location on the
electron cloud.
 The electron cloud is a visual model of the most likely
locations for the electrons. Where the cloud is denser,
there is more probability of finding an electron.
 An electron can move from one energy level to another
when the atom gains or loses energy.
Electron Cloud Model
 Electrons travel around the nucleus in random orbits.
 Scientists cannot predict where they will be at any given
moment.
 Electrons travel so fast, they appear to form a “cloud”
around the nucleus.
Electron Cloud Model
 http://www.youtube.com/watch?v=wJ2e-uPmdYg
 Atomic Theory Song:
http://www.youtube.com/watch?v=vUzTQWn-wfE
Atomic Orbitals
 An orbital is a region of space around the nucleus
where an electron is likely to be found.
 An electron cloud is a good approximation of how
electrons behave in their orbitals.
 Each orbital can contain 2 electrons.
Energy Level
Number of
Orbitals
Maximum
Number of
Electrons
1 (s)
1
2
2 (s, p)
4
8
3 (s p d)
9
18
4 (s p d f)
16
32
Isotopes
 Isotopes can be shown in several ways.
 Symbol-Atomic Mass
 H-1 (P=__, E=__, N=__)
 H-2 (P=__, E=__, N=__)
 H-3 (P=__, E=__, N=__)
 It can also be shown:
History of the Periodic Table
 Mendeleev- Father of the Periodic Table;
Arranged table according to increasing
mass.
 Moseley- Improved the table by arranging it
according to atomic number (number of
protons). There are a few places on the chart
where the mass decreases.
 Seaborg-pulled out the f block.
Arrangement of the Periodic Table
 Elements are arranged by atomic number (number of
protons).
 Each row on the periodic table is a period.
 Each column on the periodic table is a group.
 Similar electron configurations.
 Similar chemical properties.
Classes of Elements
 There are many different ways to classify elements.
 State of matter



Solids—black symbol
Liquid—blue symbol
Gas—red symbol
 Occurrence in nature
 Elements that do not occur naturally—white symbol
 General properties
 Metal
 Nonmetal
 Metalloid
Metals
 The majority of the elements on the periodic table.
 Solids (except Hg)
 Good conductors of heat and electricity
 Malleable- can be hammered into sheets
 Ductile- can be drawn into wires
 Have luster (shiny)
 Found to the left of the stairstep.
Transition Metals
 Metals in groups 3-12.
 Form a bridge between the elements on the left and
right sides of the table.
 Among the first discovered (Au, Ag, Cu)
 They form compounds with distinctive colors.
Nonmetals
 Generally have properties opposite of metals.
 Poor conductors of heat and electricity.
 Nonmetals have low boiling points—many
nonmetals are gases at room temperature.
 Brittle solids (will shatter if hit with a hammer) or
gases (b/c low boiling points)
Metalloid
 Located between metals and nonmetals---touch the




stairstep.
Have some properties of metals and some of
nonmetals.
A metalloid’s ability to conduct electric current varies
with temperature.
Si and Ge are good insulators at low temperatures, but
good conductors at high temperatures.
Semiconductors—used in computer chips.
 As you move across the period, from left to right, the
elements become less metallic and more nonmetallic
in their properties.
 Elements in a group have similar properties because
they have the same number of valence electrons.
They won’t be identical because they have different
number of energy levels.
Families
 Alkali Metals
 Alkaline Earth Metals
 Transition Metals
 Boron Group
 Carbon Group
 Nitrogen Group
 Oxygen Group
 Halogens
 Noble Gases
Alkali Metals
 They have one outer (valence) electrons so they are
very reactive.
 They are only found as compounds in nature—because
they are so reactive.
 Reactivity increases as you move down the group.
 Ex. Sodium
 Stored under oil b/c so reactive
 Makes NaCl
 Video or Na reactivity
Alkaline Earth Metals
 Have 2 valence electrons.
 Mg, Ca, Be
The Boron and Carbon Families
 Boron
 Aluminum is the most abundant metal in the Earth’s
crust.
 Bauxite is made from Al and O.
 Carbon Group
 Except for water, most of the compounds in your body
contain carbon.
 Si is second most abundant element in Earth’s crust.
 Nitrogen group—N and P in fertilizer
 Oxygen group—O most abundant
element in Earth’s crust.
 Halogens—They all have similar
chemical properties.. Very, very
reactive.
 Noble gases- colorless, odorless, and
extremely unreactive.