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Atomic Structure
Atomic Structure
• Democritus (a Greek Professor)
• First suggested the existence of tiny
fundamental particles that make up matter
• Named atoms
• John Dalton (a scientist)
• Studied the ratios in which elements combine
in chemical reactions
• Based his ideas on results of his experiments
1. All elements are composed of tiny particles called atoms.
2. Atoms of the same element are identical.
3. The atoms of a given element are different from those of any
other element
4. Atoms of one element can combine with atoms of other
elements to form compounds. A given compound always has
the same relative number and type of atoms
5. Atoms are indivisible in chemical processes. A chemical
reaction simply changes the way the atoms are grouped
together
• Symbol- H
• Gas
• Symbol- He
• Gas
• Symbol- Li
• Solid- metal
• Symbol- Be
• Solid
• Symbol- B
• Solid
• Symbol- C
• Solid
• Symbol- N
• Gas
• Symbol- O
• Gas
• Symbol- F
• Gas
• Symbol- Ne
• Gas
• Symbol- Na
• Symbol from natrium, Latin word for sodium carbonate.
• Solid
• Symbol- Mg
• Solid
• Symbol- Al
• Solid
• Symbol- Si
• Solid
• Symbol- P
• Solid
• Symbol- S
• Solid
• Symbol- Cl
• Gas
• Symbol- Ar
• Gas
• Symbol- K
• Name from Kalium, Latin word for alkali
• Solid
• Symbol- Ca
• Solid
• Protons
• Positively charged
• Found in nucleus
• Neutrons
• Neutral subatomic particles
• Found in the nucleus
• Electrons
• Negatively charged
• Found outside the nucleus (shells, energy levels, electron cloud, orbitals)
• The mass of electrons is negligible
• Atomic Number
• The number of PROTONS in the nucleus of the atom
• The atomic number identifies the element
• Atoms are electrically neutral
• # of PROTONS = # of ELECTRONS
• Mass Number
• The total number of PROTONS and NEUTRONS in the
nucleus of an atom
• How many protons, neutrons and electrons are in an atom of
Be-9?
• Protons = 4 Electrons = 4 Neutrons = 5
• How many protons, neutrons and electrons are in an atom of
Ne – 20
• Protons= 10 Electrons= 10 Neutrons= 10
• valence electrons- are the electrons in the last shell or energy
level of an atom
• Can determine by looking at the periodic table
• What is the appropriate number of valence electrons for the
following elements:
• H
• P
• F
• Ar
• C
• Allows you to see how atoms of one element will react
• Represent the atoms and the electrons in their outer energy levels.
• An electric dot diagram is the symbol for the element
surrounded by as many dots as there are electrons in its outer
energy level.
• Shows how many valence electrons there are.
• The dots are written in pairs on four sides of
the element symbol.
• Start by writing one dot on the right of the
element symbol.
• The second electron also goes on the right
• Starting with the 3rd electron, work your way
around the element symbol
X
1 2
3 6
4 7
5 8
• Use electron dot diagrams to show how atoms bond with each
other.
• A chemical bond is the force that holds two atoms together.
• Atoms bond with other atoms in such a way that each atom becomes more
stable.
• The outer energy levels will resemble those of the noble gases.
• Any “free” electron will want to be paired.
• If electrons are not paired, atom is reactive.
• If outer shell is not full, an ion may form.
• Atoms want all shells to be full and will gain/lose electrons to ensure this.
• Atoms are composed of 2 regions:
• Nucleus: the center of the atom that contains the mass of the atom
• Electron cloud (energy level): region that surrounds the nucleus that
contains most of the space in the atom
• 3-D
Nucleus Electron
Cloud
• Bohr Model of the atom:
• Reviewers think this could lead to misconceptions!
All of the protons
and the neutrons
The 1st ring can hold
up to 2 e-
The 2nd ring can hold
up to 8 e-
The 3rd ring
can hold up
to 18 e-
The 4th ring and
any after can
hold up to 32 e-
• Mass # = 12 atomic # = 6
p+ = 6 no = 6 e- = 6
6 p and 6 n live in
the nucleus
• Symbol- Cu
• Symbol - Ag
• Symbol- Au
• Symbol- Sr
• Symbol- Cs
• Symbol- Ba
• Symbol- Br
• Symbol- I
• Symbol- Ni
• Symbol- Hg
• Symbol- Fe
• Symbol- Pb
• Symbol- Zn
• Symbol- U
• Symbol- Co
• Symbol- Cr
• Symbol - Sb
• Symbol – As
• Arsenic Poisoning
• Symbol - Bi
• Symbol- Cd
• Symbol- Fr
• Symbol- Kr
• Symbol- Mn
• Symbol- Rd
• Symbol- Rn
• Symbol- Ti
• Symbol- W
• Symbol- Xe
• Atoms want to have 8 valence electrons- stable
• But not all elements have 8 valence electrons…
• Therefore some atoms become ions…
• An atom or group of atoms that have a positive or negative
charge
• An ion has either gained or lost electrons
• Cation- a positive ion has lost electron(s)
• Anion - negative ion has gained electron(s)
• In general
• metals (Mg) lose electrons ---> cations
• nonmetals (F) gain electrons ---> anions
-1 -2 -3 +1 +2
By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.
+3
• Guess the charge for the following elements:
• Mg
• K
• F
• N
Mg +2
K +1
F -1
N -3
• State the number of protons, neutrons, and electrons in each of
these ions.
•
Protons Neutrons Electrons
39
K+
19
16
O -2
8
41
Ca+2
20
Mass #
Atomic #
• Atoms of the same element that differ in the number of neutrons
in the nucleus
• Because isotopes of an element have different numbers of
neutrons, they have different mass numbers.
• To distinguish between isotopes, look at mass numbers
• Isotopes of chlorine
35
Cl 37
Cl
17 17
chlorine - 35 chlorine - 37
• Hydrogen
• 1H- Hydrogen
1
• 2H- Deuterium
1
• 3H- Tritium 1
• Carbon
• 12C
6
• 14C
6
• Two isotopes of carbon are carbon – 12 and carbon – 14.
Write the symbol for each isotope using subscripts and
superscripts. Determine the number of protons, neutrons and
electrons for each isotope
• Two isotopes of oxygen are oxygen – 16 and oxygen – 18.
Write the symbol for each isotope using subscripts and
superscripts. Determine the number of protons, neutrons and
electrons for each isotope
• A device known as a mass spectrometer can be used to
determine the relative abundance and mass of the isotopes of
elements.
• Generates a graph showing the relative amounts of each isotope found in
the examined sample.
The data can be summarized as follows: Isotope Mass` Abundance 90Zr 90.00 amu 51.5 % 91Zr 91.00 amu 11.2 % 92Zr 92.00 amu 17.1 % 94Zr 94.00 amu 17.4 % 96Zr 96.00 amu 2.80 % atomic mass of isotope 100 %
• Change each percent to a decimal by dividing by 100.
• Multiply by the mass.
• Add it all together.
• Calculate the weighted average mass of zirconium using the
data below.
•
• Isotope Mass Abundance Weighted Mass
90Zr 90.00 amu 51.5 %
91Zr 91.00 amu 11.2 %
92Zr 92.00 amu 17.1 %
94Zr 94.00 amu 17.4 %
96Zr 96.00 amu 2.80 %
