Transcript Chapter 4
Elements and the Periodic Table
8th Grade Science
Introduction to Atoms
• Greek philosopher named __________
proposed that matter is made up of tiny
particles that cannot be made any smaller
“Atomos” - means “uncuttable”
Atom - smallest particle of an element
Atomic Theory - formed in the 1600’s as a
series of models developed from experimental
• As more experiments were conducted and
evidence collected, the theory and models
Dalton’s Atomic Theory - John Dalton, English
chemist, inferred that atoms had certain
• Dalton’s atomic theory is still accepted today!
• Atoms were like smooth, hard balls that
cannot be broken down
Summary of Dalton’s Ideas page 103
• All elements are composed of atoms that cannot
• All atoms of the same element are exactly alike
and have the same ____.
• An atom of one element cannot be _________
into an atom of a different element – only
• Every ________
compound is composed of atoms of
combined in a specific
- 1897 atoms have negatively
charged electrons embedded in a positive
electrons - negatively charged particles
Rutherford and the Nucleus
• 1911 - ____________
Ernest Rutherford - a student of Thomson,
found evidence that contradicted Thomson’s
Gold Foil Experiment - beam of positively charged
particles aimed at a thin sheet of gold foil.
Most of the particles passed through the foil
as expected. However, a few particles were
Conclusions from the Foil Experiment
• Since like charges _____
repel each other,
Rutherford concluded that an atom’s
charges must be clustered in the
center of the atom.
nucleus - center of the atom
electrons - no mass
- positively charged particles that
have mass and are located in the nucleus of
- 1913, Danish Scientist, student
of both Thomson and Rutherford – electrons
move around the nucleus in certain _____
based on energy levels.
• Bohr’s Model resembles planets orbiting the
sun or layers of an onion.
Cloud of Electrons
• 1920’s – atomic model changed again
• Scientists determined that electrons DO NOT
orbit the nucleus like planets.
can be anywhere in a cloudlike region
around the __________.
electrons movement is related to its
• An _______
Energy level - specific amount of energy that it
affects the atoms reactions with
The Modern Atomic Model
James Chadwick discovered another particle in
the nucleus of atoms.
- particle discovered by Chadwick
that has no electrical charge and nearly the
same mass as _______.
Modern Atomic Model - consists of a nucleus that
contains protons and neutrons surrounded by
a cloudlike region of moving electrons.
• In an tom the number of ________
number of __________.
have a positive charge and a mass
have a negative charge and very
have neutral charge and a mass
that equals that of protons.
charge of ________
charge of _________.
Masses and Charges
• Charges balance making
the atom neutral
• Number of neutrons does
not have to equal the
number of protons
• Neutrons do not affect
the charge of an atom
because they have no
• Approximately 2,000 e⁻
equal mass of one proton.
• Every atom of an element has the same
number of _________.
- number of protons in the
nucleus of an atom.
• Atomic number identifies an _________.
Isotopes - atoms with the same number of
protons but a different number of neutrons.
of the protons and neutrons
in the nucleus of an atom.
Patterns in the Elements
Dmitri Mendelev - Russian scientist discovered a set
of patterns that applied to all elements.
Mendelev arranged the elements in order of
- organization of the elements
where the properties of the elements repeat in
each row of the table.
Henry Moseley - Brittish scientist discovered a way to
measure the positive charge on an atom’s
nucleus – the atomic number.
Periodic Table of Elements
• After Moseley’s discovery, the periodic table
was rearranged from Atomic
• Properties of an element can be predicted
based on its place in the ___________.
• Periodic table is arranged according to
Atomic number increasing from left to right.
- horizontal rows on the periodic
table where the properties of the elements
change in a set pattern.
Organization of the Periodic Table
• Elements on the left side of the periodic table are
Highly reactive metals
• Elements in the middle of the periodic table are
Less reactive metals
• Elements on the right side of the periodic table
Metalloids and non-metals
Groups - 18 vertical columns or “families” on the
periodic table with similar characteristics such as
rate of reaction. (except lanthanides and
Reading the Periodic Table
• Each element in the periodic table has all of
Atomic Number - number of protons in the nucleus
Chemical Symbol - 1 or 2 letter representation
Atomic Mass - average mass of all of the isotopes
of the element.
• Physical properties of metals:
malleability - material can be hammered or rolled
into flat sheets and other shapes.
ductility - material can be pulled out or drawn
into a thin wire
conductivity - ability of an object to transfer heat
or electricity to another object.
Mercury (Hg) - metal that is liquid at room
Chemical Properties of Metals
- the ease or speed of an element
to combine or react to other elements and
• Metals usually react by losing ________
• Sodium (Na) is very reactive where gold (Au)
and platinum (Pt) are much less reactive.
- the destruction of a metal
because of its reactivity.
Metals in the Periodic Table
reactivity of metals decreases from left to right
on the periodic table.
- metals in Group 1 on the
periodic table that react with other elements
by losing one ______.
• Alkali metals are never found in __________
elements in nature – only in compounds.
Sodium(Na) and potassium (K) - two most important
alkali metals – important for life processes.
Alkali Earth Metals
Alkali Earth Metals - Group 2 on the periodic
table that react with other metals by losing
• Not as reactive as metals in __________
more reactive than ,most other metals.
• Never found uncombined in nature.
Magnesium (Mg) and Calcium (Ca) - two most
common alkali earth metals.
Other Elements on the periodic table
Transition Metals - elements in Group 3 through
12. These metals are hard and shiny, good
conductors of electricity, less reactive than
metals in Groups 1 and 2. ________
example of a very important transition metal.
Groups 13, 14, and 15 - only some are metals
such as aluminum, tin and lead
Lanthanides - two rows of elements at the
bottom of the periodic table.
- soft, malleable shiny metals
with high conductivity.
• Lanthanides mix with other metals to form
alloy - mixture of a metal and at least one
other element, usually another metal.
- only four occur naturally on earth
– all others were created artificially. These
elements are VERY unstable. Ex. Uranium
- elements that follow uranium
that are not found naturally on Earth – when
nuclear particles are forced to crash into one
Particle accelerator - powerful machines used by
scientists to move atomic nuclei to very high
Non-metals and Metalloids
• Physical properties of non-metals:
Reactive with other elements
Dull and brittle
– Many non-metals are common elements on Earth
10 of 16
gases at room
Bromine (Br) - only non-metal that is liquid at
Chemical Properties of Non-Metals
• Atoms of non-metals usually _____
electrons with atoms that they react with.
• When metals and non-metals react,
move from the metal atoms to the
• Non-metals can also form compounds with
Families of Non-metals
• 1. _______________
- Group 14 only carbon
The Carbon Family
is a non-metal. atoms that gain, lose, or share
when reacting with other
• 2. ______________
The Nitrogen Family - Group 15 contains two
non-metals, nitrogen and phosphorous. These
atoms usually gain, lose or share _______
electrons when reacting with other elements.
• 80% of the atmosphere is nitrogen gas (N₂)
Families of Non-Metals continued
The Oxygen Family - Group 16 contains three
• 3. _____________
non-metals – oxygen, sulfur and selenium.
Elements in the oxygen family usually gain or
is highly reactive – it can combine
with nearly any other element.
most most abundant element in
• Oxygen is the ____
the atmosphere (Nitrogen is first)
The Halogen Family
• 4. ______________
The Halogen Family - Group 17 contains flourine,
chlorine, bromine, iodine, and astatine (not a
_______ means “salt forming”.
Halogen atoms usually gain or share ____
electron when it reacts with other elements.
• All halogens are __________
Very reactive and can be
dangerous to humans.
• Many compounds that contain halogens can be
useful to humans – salt, flourine in water, calcium
Noble Gases - elements in Group 18 that do not
ordinarily form compounds because atoms of
noble gases do not usually gain, lose, or share
• These gases are usually ___________.
• All of the noble gases exist in the Earth’s
• Noble gases were not discovered until late 1800’s
because they are _______
unreactive and ________.
Hydrogen (H) - in the upper left corner of the
• Hydrogen makes up more than 90%
___ of the
atoms in the universe.
• Hydrogen is rarely found as a ___________.
- along the border between
metals and non-metals.
• There are ___
metalloids and they have
characteristics of both metals and non-metals.
• All metalloids are solid
____ at room temperature.
• Metalloids are also brittle, hard, somewhat
reactive, varying ability to conduct heat and
Silicon (Si) - most common metalloid
Semi-conductors - substances that conduct
electricity under some conditions but not
metalloids are used as semiconductors
because of their physical properties.
• Semiconductors are used to make _________,
Radioactive Decay - the atomic nuclei of unstable
isotopes release fast moving particles and energy.
- French scientist in 1896
discovered the effects of radioactive decay while
he was studying a mineral that contained
Marie Curie is the
- named after __________
spontaneous emission of radiation by an unstable
nucleus such as uranium.
Types of Radioactive Decay
• Natural radioactive decay can produce
Alpha decay - an alpha particle consists of two
protons and two neutrons and is positively
charged. The release of an alpha particle by an
atom is decreases the atomic number by __
and the atomic mass by __
- a neutron inside of the nucleus
of an unstable atom changes into a negatively
charged beta particle and a proton.
Beta particle - fast moving electron given off
by a nucleus during radioactive decay.
• Nucleus has one _____
neutron and one ____
proton – therefore, the atomic mass stays the
same but the atomic number increases by __
Gamma Radiation - consists of high-energy
waves – has no charge and does not cause a
change in either atomic mass or atomic
Effects of Nuclear Radiation