Chapter 4 Atomic Structure - Henry County School...
Transcript of Chapter 4 Atomic Structure - Henry County School...
Subatomic particles of the atomAtoms are the building blocks of all
Matter.
Atoms are mostly empty space with
a small dense core known as the
Nucleus.
Atoms are made up of 3 smaller
particles (Subatomic Particles) :
Protons, Neutrons, and Electrons
Nucleus Makes up most of the
mass of the atom.
Made up of the following
subatomic particles:
Protons: positively
charged
Neutrons: neutral particles
Has an overall + charge.
Protons
positively charged;
Located inside nucleus;
gives the atom its identity
has the mass of 1atomic mass unit (amu)
Same size as a neutron (1amu)
Protons + Neutrons = the mass of the
atom (atomic mass)
Neutrons
neutral charge;
inside nucleus;
has the mass of 1atomic mass unit (amu)
Same size as a proton (1amu)
Protons + Neutrons = the mass of the
atom (atomic mass)
Electrons negative charged
has the mass of 1/1840
**note- electrons are extremely small compared to
Protons & Neutrons
Located in the electron cloud
Electron Cloud- Area outside the nucleus
where you are most likely able to find a
nucleus.
Subatomic ParticlesParticle Charge Mass Location
Electron
(e-) -1 1/1840 amu Electron
cloud
Proton
(p+) +1 1 amu Nucleus
Neutron
(no) 0 1 amu Nucleus
Amu= atomic mass unit= a unit used to measure the particles of an atom. = 1/12th the
mass of a carbon atom
Atomic Number
Elements are different because they contain
different numbers of PROTONS.
The number of Protons gives the atom its
identity.
The “atomic number” of an element is the
number of protons in the nucleus.
Atomic Number
(# of protons)
What makes an Atom Neutral? When an atom has the same number of protons
as electrons. (+) = (-)
if the atom is neutral then it has not lost or
gained electrons.
Atomic charge- an atom will have a charge when
the protons and the electrons are not equal in
number. Atoms will lose or gain electrons to
become charged.
Atoms that have a charge are called ions.
Example: A sodium atom has 11 protons and 10
electrons. What is the charge? +11 protons (+)
-10 electrons (-)
--------------------Subtract
+1 charge
2 Protons (+)
6 Electons (-)
------------------------
-4 charge
What is the Charge of these atoms?
Which one is an Ion?
6 Protons (+)
6 Electons (-)
------------------------
0 charge**** Ion ****
Isotopes Atoms of the same element can have
different numbers of neutrons.
Thus, different mass numbers.
These are called isotopes.
Isotopes are atoms of the same
element having different masses,
due to varying numbers of neutrons. Elements occur in nature as mixtures of
isotopes.
How to Name Isotopes
Write the name then put the
mass number after the name
of the element:
carbon-12 shorthand: C-12
carbon-14 shorthand: C-14
uranium-235 shorthand: U-235
Isotopes are atoms of the same element having
different masses, due to varying numbers of
neutrons.
Isotope Protons Electrons Neutrons Nucleus
Hydrogen–1
(protium) 1 1 0
Hydrogen-2
(deuterium) 1 1 1
Hydrogen-3
(tritium)
1 1 2
The 3 Isotopes of Hydrogen
Mass number vs Atomic Mass Atomic Mass- Atomic mass is the
average of all the naturally
occurring isotopes of that element. the decimal you see on the periodic table
An average of all the isotopes of that element.
Mass number- the number of
protons and neutrons in the
nucleus of a specific isotope The mass of that specific isotope.
Atomic
Mass
Mass Number
Mass number is the number of
protons and neutrons in the nucleus
of an isotope:
Neutrons = Mass # - p+
Mass # = p+ + n0
Nuclide p+ n0 e- Mass #
Oxygen - 10
- 33 42
- 31 15
8 8 1818
Arsenic 75 33 75
Phosphorus 15 3116
Complete Symbols Aka: Isotope Notation
Contain the symbol of the element,
the mass number and the atomic
number.
XMass
number
Atomic
numberSubscript →
Superscript →
Symbols
Find each of these:
a) number of protons
b) number of
neutrons
c) number of
electrons
d) Atomic number
e) Mass Number
Br80
35
Symbols
If an element has an atomic
number of 34 and a mass
number of 78, what is the:
a) number of protons
b) number of neutrons
c) number of electrons
d) complete symbol
Symbols
If an element has 91
protons and 140 neutrons
what is the
a) Atomic number
b) Mass number
c) number of electrons
d) complete symbol
Symbols
If an element has 78
electrons and 117 neutrons
what is the
a) Atomic number
b) Mass number
c) number of protons
d) complete symbol
Complete Symbols of an ION
If the symbol has a superscript on
the right side, it has lost or gained
electrons.
XMass
number
Atomic
numberSubscript →
Superscript → # of electrons
lost or gained
• Negative number = #
of electrons it has
gained
• Positive number = #
of electrons it has lost
Atomic Mass How heavy is an atom of oxygen?
It depends, because there are different
kinds of oxygen atoms.
We are more concerned with the average
atomic mass.
This is based on the abundance
(percentage) of each variety of that
element in nature.
We don’t use grams for this mass because
the numbers would be too small.
Measuring Atomic Mass
Instead of grams, the unit we use is the Atomic Mass Unit (amu)
It is defined as one-twelfth the mass of a carbon-12 atom.
Carbon-12 chosen because of its isotope purity.
Each isotope has its own atomic mass, thus we determine the average from percent abundance.
To calculate the average:
Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.
If not told otherwise, the mass of the isotope is expressed in atomic mass
units (amu)
Atomic Masses
Isotope Symbol Composition of
the nucleus
% in nature
Carbon-12 12C 6 protons
6 neutrons
98.89%
Carbon-13 13C 6 protons
7 neutrons
1.11%
Carbon-14 14C 6 protons
8 neutrons
<0.01%
Atomic mass is the average of all the
naturally occurring isotopes of that element.
Carbon = 12.011
Practice Problem:
Element X has 2 Natural occurring isotopes. Isotope 10X has the
mass of 10.012 and a relative abundance of 19.91% . The other
istotope 11X has the mass of 11.009 and the abundance of 80.09%.
Calculate the average atomic mass of this element.
Mass X Abundance (changed to a decimal)
10X: 10.012amu X 0.1991 = 1.993 amu11X: 11.009amu X 0.8009 = 8.817 amu
---------------------------------------------------Add--------------
Average Atomic Mass = 10.810 amu
The Periodic Table:
A Preview
A “periodic table” is an
arrangement of elements in which
the elements are separated into
groups based on a set of repeating
properties
The periodic table allows you to
easily compare the properties of
one element to another
The Periodic Table:
A Preview
Each horizontal row (there are 7 of
them) is called a period
Each vertical column is called a
group, or family
Elements in a group have similar
chemical and physical properties
Identified with a number and
either an “A” or “B”
More presented in Chapter 6