Download The Atom - Pleasantville High School

The Atom
Welcome to Discovery Education
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• What is an element?
• What are the subatomic parts of an atom?
An atom
• Basic unit of matter, “unable to be cut”
• Element
• Pure substance entirely of one atom
What are the Subatomic
Particles?
•
•
•
•
Name three and their charges?
Proton
Neutron
Electron
The Atom
Cloud of negative
charge (2 electrons)
Electrons
Nucleus
(a)
(b)
Who is Neils Bohr?
• He proposed a theory stating:
• an atom is composed of a dense nucleus
with electrons in its surrounding orbit
• The electrons must have a certain amount
of energy to orbit the nucleus.
• Suggests that electrons more in a fixed
manner around the nucleus.
Modern Atom Model
• Electron cloud model
• Protons have a mass: 1.67 x 10-24 g
• Mass is so small, units atomic mass unit
(1 amu)
• Atomic number: number of protons, of the
same element the protons must be the same
• Electrons: are equal to but have an opposite
charge to that of a proton
– Less mass 1/1836 amu
• Mass number: sum of the protons and neutrons
Atomic Structure
15 N
7
Mass number = protons plus neutrons
If mass number is 15, how many protons do you
have if you have 8 neutrons?
Atomic number = number of protons
* If the atom is neutral the protons and electrons
are equal!
If the mass number is 15 and there is no charge
and the atomic number is 7 how many electrons
and neutrons do you have?
Atomic Structure Continued!!
• Atomic Number
– The number of protons in the nucleus of an
atom
– Determines which element
• Mass Number
– The number of nucleons (protons + neutrons)
– If you don’t know the mass number you can
round off the atomic mass for that element
• # neutrons = mass # - atomic #
• The atomic number cannot change. Mass number
can.
Element Atomic Atomic
Number Mass
Mass #
Protons Neutron Electron
s
s
Element Atomic
#
Atomic
Mass
Mass
Protons Neutron Electro
Number
s
ns
Each electron in an atom has
its own distinct amount of
energy.
When electrons are in their lowest energy
state, it is called the ground state
The ground state for Na is 2-8-1
Tom Lehrer's "The Elements". A
Flash animation by Mike Stanfill,
Private Hand
II. Periodic Table
• elements: Periodic Table are arranged in increasing
atomic number.
• Placement or location of elements on the Periodic Table
indicates the physical and chemical properties of that
element.
• Number of protons in an atom (atomic number) identifies
the element
• Atomic mass: found on the Periodic Table of the
Elements
Classifying Elements
• Metals
• Nonmetals
• metalloids or semimetals
(B, Si, Ge, As, Sb, Te),
• noble gases
Metals on
the left
Nonmetals
on the right
Metalloids
semimetals
Average atomic mass of an element . . .
- the weighted average of the masses of its
naturally occurring isotopes
Isotope Mass Abundance
Calculation
12C
12
98.89%
12 x .9889 =
13C
13
1.108%
13 x 0.01108 = 0.1440
Atomic Mass (weighted average)
11.87
12.01 amu
Isotopes
• Isotope: identified by the sum of the protons and
neutrons in an atom = (mass number)
• Isotope: atom of the same element having same number
of protons but different number of neutrons
14C,
carbon-14, C-14
C-12 isotope
C-13 isotope
C-14radioactive
Density=mass/volume
A physical property is one which does not change the
identity of the substance when tested.
Differentiation of Elements
• physical properties differentiate elements by their
Physical properties
• ex: density, conductivity, malleability, solubility, and
hardness, differ
• Elements can be differentiated by chemical properties
too.
• Chemical properties describe how an element behaves
during a chemical reaction.
When testing a chemical property, the substance may change into another
substance.
Some elements exist in two or more forms in
the same phase. These forms differ in their
molecular or crystal structure, and hence in
their properties. These are called allotropes.
Allotropes of oxygen
Allotropes of carbon
Oxygen ( O2 )
Graphite
Ozone ( O3 )
Diamond
Buckminsterfullerene
allotropes
• Some elements exist in two or more forms of the same
phase.
• They differ in molecular or crystal structure, and in
properties.
Comparing the physical properties of metals
and nonmetals
Nonmetals
Metals
•
•
•
•
•
Silvery gray color except copper •
and gold
Solid at room temperature except
mercury
Good conductors of heat and
•
electricity
Malleable – can be hammered into
shapes (thin sheets)
Ductile – can be pulled into wires
•
•
Many different colors
–
–
–
–
Sulfur – yellow
Chlorine – green
Bromine – orange
Iodine - purple
Many different states (phases)
– H, N, O – gas
– Br – liquid
– S, C, I – solid
Poor conductors of heat and
electricity (except carbon)
Brittle – breaks when hit
All elements are solid at room temperature
except for the following:
Liquids
• Mercury (Hg) - the only
liquid metal at room
temperature
• Bromine (Br) - the only
liquid nonmetal at room
temperature
Gases
•
•
•
•
•
•
Hydrogen (H)
Oxygen (O)
Nitrogen (N)
Fluorine (F)
Chlorine (Cl)
All of group 18 (noble
gases)
Helium (He), Neon (Ne) Argon
(Ar), Krypton (Kr), Xenon (Xe),
Radon (Rn)
• For Groups 1, 2, and 13-18 on the Periodic Table,
elements within the same group have the same number
of valence electrons (helium is an exception) and
therefore similar chemical properties.
Group numbers and family names
• Group 1
Alkali Metals
– Very reactive metals, always found as compounds in nature
– 1 valence electron - lose 1 electron to form +1 ions
• Group 2
Alkaline Earth Metals
– Reactive metals, always found as compounds in nature
– 2 valence electrons - lose 2 electron to form +2 ions
• Group 17
Halogens
– Reactive nonmetals
– 7 valence electrons - gain 1 electron to form –1 ions
• Groups 18
Noble Gases
– Not reactive – do not form ions
– Filled, stable valence shell (8 electrons except He which has
2)
The succession of elements within the same
group demonstrates characteristic trends:
differences in atomic radius, ionic radius,
electronegativity, first ionization energy,
metallic/nonmetallic properties.
Going down a group, there are more shells
separating the nucleus from the valence
electrons
Reference Table S
Trends in Atomic Radius
• Atomic Radius – half the distance
between two nuclei
• Going down a group, the atomic radius
increases because there are more
principal energy levels (shells)
• Going across a period, the atomic
radius decreases because there are
more protons pulling the valence shell
closer
Atomic Radius
The succession of elements across the same
period demonstrates characteristic trends:
differences in atomic radius, ionic radius,
electronegativity, first ionization energy,
metallic/nonmetallic properties.
Going across a period, there are more protons
pulling on the valence electrons
Forming Ions – making atoms
happy
• Atoms gain or lose electrons to complete their
outer shell
– A noble gas configuration
– A complete octet
– 8 electrons
• Metals lose electrons to form positive (+) ions
• Nonmetals gain electrons to form negative (-)
ions
• Ionic Radius
– A negative ion is always larger than its original
atom.
– A positive ion is always smaller than its original
Ionic Radius in Metals
• Sodium (Na) is a metal
– Electron configuration 2-8-1
• (11 protons and 11 electrons)
– Loses 1 electron in its valence shell
– A sodium atom becomes a sodium ion
• Na+
• 2-8 (10 electrons but 11 protons)
– Same electron configuration as a noble gas
(Ne) but has more protons. Electrons are
pulled in much closer so the radius
decreases.
Ionic Radius in Nonmetals
• Chlorine (Cl) is a nonmetal
– Electron configuration 2-8-7
Notice-name of
negative ions end
in IDE
• (17 protons and 17 electrons)
– Gains 1 electron in its valence shell
– A chlorine atom becomes a chloride ion
• Cl• 2-8-8 (18 electrons but only 17 protons)
– Same electron configuration as a noble gas
(Ar) but has fewer protons. Electrons repel
each other and the radius increases.
• 2- ions are even larger than – ions