Download 1.2--NOTES--Basic Atomic Structure

2.1: Basic Atomic Structure
8/18/16
Part I: Subatomic Particles
• subatomic particle = a particle found inside the atom. There are 3
types of subatomic particles:
Name
Charge Symbol
Location
Mass
proton
+1
p+
in the nucleus
approx. 1 amu (1.007 amu)
neutron
0
n0
in the nucleus
approx. 1 amu (1.008 amu)
electron
-1
e-
in electron cloud 0.000 549 amu (negligible)
• all atoms of all the different types of elements contain these same
basic parts
• what makes one element different from another? The proton number.
• all atoms of the same element have the same proton number, and
atoms of different elements have different proton numbers.
• ex: all gold (Au) atoms have 79 protons.
79 ≠ 47, so
all silver (Ag) atoms have 47 protons.
gold ≠ silver
• ex: all gold (Au) atoms have 79 protons.
79 ≠ 47, so
all silver (Ag) atoms have 47 protons. gold ≠ silver
• neutron number varies with the type of isotope (more on this later)
• electron number is the same as proton number for uncharged
(neutral) atoms (also, more on this later)
What makes one element
different from another?
the number of protons it
has in its nucleus
What does negligible
mean?
able to be ignored
(in the atom’s mass)
• ex: all gold (Au) atoms have 79 protons.
79 ≠ 47, so
all silver (Ag) atoms have 47 protons. gold ≠ silver
• neutron number varies with the type of isotope (more on this later)
• electron number is the same as proton number for uncharged
(neutral) atoms (also, more on this later)
Part II: Atomic Structure
• the atom has two distinct areas: the nucleus and the electron cloud.
• nucleus = center of the atom (like the core of the earth) where the
protons and neutrons are found.
• the nucleus is positively charged. Why? Because of the presence
of protons (see table in Part I above).
• the nucleus is the area of the atom with the most density
• remember, density = mass/volume
D=m
• look at the masses in the table in Part I above
V
• the nucleus is the area of the atom with the most density
• remember, density = mass/volume
D=
• look at the masses in the table in Part I above
• protons and neutrons are very heavy in
relation to electrons (high mass)
• the area itself is very small (low volume)
• high mass/low volume = high density
m
V
What two subatomic
particles are found in the
nucleus?
protons and neutrons
The nucleus is a very
(small, large) area inside
the atom.
• the nucleus is the area of the atom with the most density
• remember, density = mass/volume
D=m
• look at the masses in the table in Part I above
• protons and neutrons are very heavy in
V
relation to electrons (high mass)
• the area itself is very small (low volume)
• high mass/low volume = high density
• electron cloud = area surrounding the nucleus where the electrons are
found, spinning very fast around the nucleus.
• the exact location of any particular electron cannot be known
because of their high speed, but we do know that…
• electrons spin a distinct, confined distances
from the nucleus (like planets have distinct
orbits around the sun). We call these
distinct distances from the nucleus
“energy levels.”
• electrons spin a distinct, confined distances
from the nucleus (like planets have distinct
orbits around the sun). We call these
distinct distances from the nucleus
“energy levels.”
• energy level = a distinct distance from
the nucleus where an electron can be
found, spinning.
• each energy level holds a different
amount of electrons:
• 1st energy level holds 2 (total)
• 2nd energy level holds 8 (total)
• 3rd energy level holds 18
(8 outer, 10 inner)
• 4th energy level holds 32 (8 outer, 24 inner)
• the 5th – 7th energy levels hold even more than that
• each energy level holds a different
amount of electrons:
• 1st energy level holds 2 (total)
• 2nd energy level holds 8 (total)
• 3rd energy level holds 18 (8 outer, 10 inner)
• 4th energy level holds 32 (8 outer, 24 inner)
• the 5th – 7th energy levels hold even more than that
• in an electron dot diagram (AKA energy level diagram), only
the outer electrons are shown.
• notice how the energy levels always contain paired, evenly
distributed electrons.
• Mg needs 12
electrons
• 2 electrons on the
1st level
• 8 electrons on the
2nd level
• 2 electrons on the
3rd level
• 2 + 8 + 2 = 12
electrons total
• S needs 16
electrons
• 2 electrons on the
1st level
• 8 electrons on the
2nd level
• 6 electrons on the
3rd level
• 2 + 8 + 6 = 16
electrons total
• N needs 7
electrons
• 2 electrons on the
1st level
• 5 electrons on the
2nd level
• 0 electrons on the
3rd level
• 2 + 5 = 7 electrons
total
The high speed at which
electrons spin prevents
us from knowing the
exact ________
position of any
electron.
What do the “rings” on an
electron dot diagram
represent?
energy levels
Electrons on the second
energy level are drawn
(N/S/E/W, diagonally).
Why?
to keep electrons from
overlapping
(being too close)
Part III: Atom Symbols & Numbers
•all elements are represented by either 1- or 2-letter symbols.
• most match the name of the element, others
come from old names or other languages.
• all symbols must either be one capital letter, or
one capital and one lowercase.
•atomic number = number of p+. Written in bottomleft-hand corner of symbol. Identifies the element.
•mass number = number of p+ & n0. Identifies the isotope.
Written in top-left-hand corner.
•average atomic mass = weighted average of all the mass numbers of
all the isotopes of an element. Not written on symbol, but is found on
PT.
•another number you can find on a symbol of an element is the charge.
• it will be located in the top right-hand corner of the symbol.
• we will discuss charge in more detail later.
Name an element whose
symbol and name do not
“match.”
Na = sodium,
K = potassium,
Fe = iron
Cu = copper
Ag = silver
Sb = antimony
W = tungsten
Au = gold
Hg = mercury
Pb = lead
96
42
Mo
What is this element’s
42 What is
atomic number? ___
its mass number? ___
96
Name? molybdenum
____________
True or False? The mass
number and the average
atomic mass of an
element are the same.
False!
The mass number
identifies the (element,
isotope). The atomic
number identifies the
(element, isotope).
Part IV: Isotopic Notation
•isotope = atoms of the same element that have the
different numbers of neutrons.
• this means their proton number (atomic number) is
the same, but because the number of neutrons differs, the result
is different mass numbers for each isotope.
• ex: the isotope shown above is carbon-14. The other isotopes
of carbon are carbon-12 and carbon-13.
•to find the neutron number of different isotopes,
simply subtract the atomic number from the
mass number.
mass number
– atomic number
neutron number
PRACTICE: Fill in the info that is missing, per isotope.
Name of Isotope
Symbol
Atomic
Number
Mass
Number
9
# of
Neutrons
# of
Protons
10
66Zn
sodium-23
40
________-32
Remember:
mass number
– atomic number
neutron number
20
16
mass number
– neutron number
atomic number
atomic number
+ neutron number
mass number
PRACTICE: Fill in the info that is missing, per isotope.
Name of Isotope
Symbol
Atomic
Number
fluorine-__
19
zinc-66
19
F
9
sodium-23
calcium-40
sulfur
________-32
66Zn
23Na
40Ca
32S
Remember:
mass number
– atomic number
neutron number
30
11
20
16
Mass
Number
19
66
23
40
32
mass number
– neutron number
atomic number
# of
Neutrons
10
36
12
20
16
# of
Protons
9
30
11
20
16
atomic number
+ neutron number
mass number