Download File - 8th Grade Physical Science

Atoms and the
Periodic Table
High School Physical Science
Mr. Brock
GPS Connections
GPS Standards:
S8P1 Students will examine the
scientific view of the nature of
matter.
S8P1a: Distinguish between atoms
and molecules.
S8P1f: Recognize that there are
more than 100 elements and
some have similar properties as
shown on the Periodic Table of
Elements.
2
Atoms – the historical view



The word "atom" comes from the Greek atomos
and signifies "indivisible". This notion was
invented by Leucippe of Milet in 420 BC.
Democritus (c. 460 – 370 BC) promoted the
theory that all nature could be understood in
terms of the movement of atomos.
In ancient times, many elements were known,
including C, S, Cu, Ag, Au, Fe, Sn, Sb and Pb.
The names of most of these are from the Latin
words.
3
History of Atomic Theory
John Dalton (1766-1844) proposed the Atomic
Theory in 1803 which stated that:
 All matter is composed of atoms
 All atoms of the same element are identical
 Atoms of different elements are different
 Atoms unite in definite ratios to form
compounds
4
History (continued)

Dimitri Mendeleev’s periodic table
(1869) classified and sorted
elements based on common
chemical properties. His table had
62 known elements, and left space
for 20 elements that were not yet
discovered. The elements were
arranged in order of atomic number.
The discovery of atoms to fill the
blank spaces proved that his
periodic table was a good model.
5
History (continued)


The electron was discovered in 1897 by
J.J. Thomson. He imagined the atom as a
“raisin pudding” with electrons stuck in a
cake of positive charge.
In 1912, Ernest Rutherford
discovered the nucleus by doing
scattering experiments. He concluded
the atom was mostly empty space,
with a large dense body at the center,
and electrons which orbited the
nucleus like planets orbit the Sun
6
History (continued)


Rutherford also realized that the nucleus must contain both
neutral and positively charged particles. From
experiments, he concluded that the nucleus was a hard
small sphere, and that most of the atom was empty space
by how the alpha-particles behaved.
The neutron was then discovered in 1932 by James
Chadwick.
7
Vocabulary – Parts of an Atom




Electron: negatively charged fundamental
particle
Proton: positively charged fundamental
particle
Neutron: uncharged fundamental particle
Nucleus: small, central unit in the atom that
contains neutrons and protons
8
Parts of an Atom

Each element in the Periodic Table has a different number of
protons in its nucleus



p
The element also has the same number of electrons




Protons have positive charge
Change the number of protons  change elements
Electrons have negative charge
Change the number of electrons  ionize the element
This is called chemistry
e
Most elements also have neutrons


Neutrons have no charge
They are in the nuclei of atoms
n
9
Atomic Structure
Each atom is shown on the
periodic table with clues to
its atomic structure.


Atomic Number (top) – tells how many
protons (+) in an atom’s nucleus. Oxygen has
8 protons.
Atomic Mass (bottom) – This is the average
mass of an element’s atoms. It is equal to the
combined total of neutrons & protons in an
atom’s nucleus.
10
Determining Atomic Structure
Protons: The atomic
number tells
number
Neutrons: Subtract
Atomic Number
from Atomic Mass
Electrons: Same
number as Protons
Oxygen
Protons: 8
Neutrons: 16 – 8 = 8
Electrons: 8
11
Try this!
Name: ?
Symbol: ?
How many:
Protons ?
Neutrons ?
Electrons ?
12
Answers:
Name: Fluorine
Symbol: F
How many:
Protons: 9
Neutrons: 10
Electrons: 9
13
More questions:



What is an element?
Why are nuclei and
atoms stable?
What is a molecule?
14
Key Concepts and Vocabulary: Atoms,
Elements and Molecules



Atom: smallest unit of an element
Element: any of more than 100 fundamental
substances that consist of atoms of only one kind
Molecule: a collection of atoms, bound together.


Molecules can be made from only one element, such
as H2 or O2
Molecules can be made from different elements, such
as H2O or CO2
15
Isotopes





A variant form of an element that has similar
structure but different mass.
Isotopes are atoms that have the same number of
protons (atomic number is the same), but a
different number of neutrons (atomic mass is
different).
If it looses protons, it becomes a different
element.
Each element has a limited number of isotopes
that occur naturally.
Some isotopes are unstable and radioactive.
16
Ions



Ions are atoms with an
electrical charge. This charge
comes from either losing or
gaining electrons.
They have the same number of
neutrons and protons.
They carry an electrical
charge.
17
History of the atom (Part 2)


Following Ernest Rutherford’s planetary model of
the atom, it was realized that the attraction
between the electrons and the protons should
make the atom unstable
In 1913 Niels Bohr proposed a model in which
the electrons would stably occupy fixed orbits, as
long as these orbits had special locations.
18
History of the atom (continued)

In the Bohr model, electrons occupy
specific “orbits,” but can change orbits,
accompanied by the absorption or
emission of a photon of a specific color
of light (remember this when we study
light!)
19
History of the atom (continued)

Modern theories lead to the theory that
there are stable locations of electrons,
which are not exact planetary orbits, but
are characterized by specific numeric
values.

Each electron shell is
characterized by a different
principle quantum number,
usually called n.
20
History of the atom (continued)


In quantum theory, the
electron shells are not fixed
orbits, but clouds of
probability. You can’t
measure the exact location
of the electron.
Each electron orbital cloud
has a different shape, and no
two electrons can be in the
same orbital (unless they
have opposite spins.)
21
Periodic Table of the Elements
Review: What
are the numbers
in each box?
22
Navigating the Periodic Table


The rows (across) are the “periods”
 Each period starts a new shell of electrons
 The periods are numbered starting with 1 at
the top
The columns (up and down) are the “groups”
 Each group has similar chemical properties
 The groups are numbered starting with 1 at
the left
 Elements with similar properties have the
same number of electrons in the outermost
shell (or orbital). These are called valence
electrons.
23
Electron Shells & Atomic Structure
The first shell will hold up
to two electrons. The
orbital is spherical, and
called 1s. The first row
of the periodic table
consists of 2 elements
with 1s electrons.
Hydrogen has 1
electron in this shell,
Helium has 2.
24
Electron Shells &
Atomic Structure (continued)
Atoms in the second (and
third) rows of the Periodic
Table each add up to eight
electrons in “P” orbitals.
The shells that are filled are made of
 a spherical orbital that holds 2 electrons, called 2s
(second row) or 3s (third row), and
 3 non-spherical orbitals that hold a total 6
electrons, called 2p (second row) or 3p (third row).
25
Electron Shells &
Atomic Structure (continued)
Look at a copy of the periodic table. The elements
which have the same number of electrons in their
outer orbitals (valence electrons), are in the same
“family” and have similar characteristics,
depending on the number.
 Group 1: 1 valence electron – Alkali Metals
 Group 2: 2 valence electrons – Alkali Earth Metals
 Group 17: 7 valence electrons – Halogen Family
 Group 18: 8 valence electrons (2 Helium – outer
shell is filled) – Noble Gases
26
Shell structure
e




Carbon=C
Sodium=Na
Neon=Ne
Chlorine=Cl
p
p
p
e
e
Review:
what is this
element?
How many protons and electrons do these
elements have?
How many orbitals? How many electrons in
each? How many valence electrons?
27
Shell structure: thinking deeper
Atoms with full outer shells are the most stable. They
do not gain or lose electrons easily. Where are the
elements with very stable outer shells in the
periodic table?
Atoms will combine best in ways that make them
more stable – fill their outer shells. This is called
“valence”or chemical bonding. The two ways this
can occur are by:

Ionic bonding – transferring electrons

Covalent bonding – sharing electrons
Look at your periodic table. Notice the number of
valence electrons in each family. How will atoms
most likely combine to become stable?
28
Key concepts: Periodic Table




The number of elements in each of the rows
(periods) in the periodic table, are due to the rules
that relate to the electron orbitals.
In columns (groups) in the periodic table, similar
chemical properties are due to the number of
valence electrons in filled or unfilled shells.
Completely filled shells make an atom very stable
Elements with 1 or 2 electrons outside of filled
shells or with 1 or 2 missing electrons are very
chemically reactive. They always try to combine
with other elements that can fill their shells.
29
Important Dates




Tuesday 8/23 Notes Quiz-you will need
your device
Tuesday 8/23 Begin “Periodic Table Basics
Project”-Due on Friday 8/26
Wednesday 8/24 Vocabulary Quiz- you will
need you device
Friday 8/26 What kind of Families are in
the neighborhood project poster
introduction
30