Download electrons = # protons

Topic 1
The Atom
Topic 1-Outline
1.
Parts of the Atom
a. Proton
b. Neutron
c. Electron
d. Rutherford’s Gold Foil Experiment
2. The Structure of the Atom
a. Mass number
b. Number of protons
c. Number of neutrons
d. Number of electrons
e. Atomic number
f. Ions
3. Isotopes
4. Atomic Mass
-be able to calculate
5. Electron Configuration
a. Know the diagonal rule
b. Three methods
c. Ground state vs. excited state
6. Types of Matter
a. Homogeneous vs. heterogeneous matter
b. Pure Substances
c. Mixtures
d. Distinguishing between mixtures and compounds
i. Filtering
ii. Chromatography
iii. Distillation
Definitions/Terms to Know
1. Proton
A positively charged subatomic particle
found in the nucleus of an atom.
It has a mass of 1 amu and
a positive charge
2. Neutron
A subatomic particle with no (neutral)
charge and a mass of 1 amu;
found in the nucleus of an atom
3. Nucleons
Protons + neutrons in the nucleus
of an atom
4. Electron
A negatively charged subatomic particle found
orbiting around the nucleus.
It has no mass and a negative charge
In the modern theory,(aka the wave-mechanical model)
the electron has both properties of a wave and particle.
This is referred to as the wave-particle duality of
the electron
Models of the Atom
1. Dalton (1803)-pictured atoms as tiny, indestructible
particles, with no internal structure.
2. Thomson (1897)-electrons embedded in a sphere of
positive electrical charge
Plum pudding model
3. Rutherford (1922)-finds that an atom has a
small, dense, positively charged nucleus.
Electrons move around the nucleus.
Atom is mostly empty space.
Never mentions neutrons.
Rutherford’s Gold Foil Experiment
An atom is mostly empty space.
It consists of a positively charged,
dense center (nucleus) with
electrons found orbiting the nucleus.
He never mentioned neutrons.
4. Bohr (1913)-the electrons move in circular
orbits at fixed distances from the nucleus
5. Schrodinger (1926)-describes the motion of electrons
in atoms. His work leads to the electron cloud model.
Orbital-region of space in which
there is a high probability
of finding an electron
The Atom
Mass Number
Equal to the # protons + # neutrons
Must be a whole number
Equal to the atomic mass rounded to the
nearest whole number
Number of Protons
Equal to the atomic number
Is also the nuclear charge
How to find the number of protons, electrons, neutrons,
atomic number, mass number
# protons = atomic number (look on Periodic Table)
# neutrons = mass number - # protons
mass number = # protons + # neutrons
or
atomic mass rounded to nearest whole number
(depending on the information given)
# electrons = # protons (if neutral)
Atomic mass = look on Periodic Table
The weighted average of the masses of the
naturally occurring isotopes of the element
Element Notation
4 different ways of element notation
1.
2. 4He
3. He-4
4. Helium-4
Ion-an atom or group of atoms that has a
positive or negative charge
Negative ion (anion)-gained electrons
ex. S-2-gained 2 electrons
PO4-3-gained 3 electrons
Positive ion (cation)-lost electrons
ex. Fe+3-lost 3 electrons
NH4+1-lost 1 electron
Isotope-atoms of the same element that have the same atomic
number (same # of protons) but different mass number
due to a different number of neutrons
Element/Ion
C-12
C-13
C-14
6
#p
6
#n
6
7
8
#e
6
6
6
Atomic mass
12.011
12.011
12.011
6
At. #
6
6
6
Mass #
12
13
14
So…let’s put it all together and attempt to fill
in a chart
Element/ Atomic Atomic # p
Ion
Mass No.
#n
#e
Mass
No.
Ca
40.08
20
20
20
20
40
Sb
121.760
51
51
71
51
122
N-3
14.0067
7
7
7
10
14
127.60
52
52
76
46
128
Te+6
Watch out for isotopes. The atomic mass and the
mass number will not correspond to each other
Element
Ar-36
Mass
#
36
Atomic
Mass
39.948
Ar-38
38
Ar-40
40
#p
#n
#e
18
18
18
39.948
18
20
18
39.948
18
22
18
Remember our definition of atomic mass-the weighted
average of the masses of the naturally-occurring
isotopes of that element.
So…how do they determine an atomic mass?
Ex. Cl-35 has an abundancy of 75.77 % and
Mass of 34.969
Cl-37 has an abundancy of 24.23% and
Mass of 36.966
Since it is a weighted average:
(34.969)(75.77) + (36.966)(24.23)
100
= 35.454
Check your periodic table now!
It becomes important to chemists to know
the location of an atom’s electrons.
The location of an atom’s electrons is called
electron configuration
There are 3 methods:
1. Diagonal Method
2. Arrow Method
3. Lewis Dot
All three methods depend on the fact that you know
The Diagonal Rule
The Diagonal Rule
What does each number/letter represent?
Principle
Energy level 
(1-7)
6
5p
^
Sublevel
(s, p, d or f)
<
Maximum no. of
electrons
(can have less)
KernelThe part of the atom exclusive of its valence electrons
(the nucleus + all inner electrons)
Valence electrons-
The electrons in the outermost shell (valence shell) of an atom
Ground state
The condition of an atom or ion in which the electrons
occupy the lowest available energy levels
Excited state
The condition that exists when the electrons
of an atom occupy higher energy levels while lower
energy levels are vacant
Ground state
Excited state
How does an electron become excited?
Electrons absorb energy and temporarily move
to a higher energy level. The electron quickly returns
to a lower available level emitting the same amount of
energy it absorbed to go to the higher energy level.
This energy is seen as light.
While the light appears as one color, it is actually
composed of many different wavelengths, each of
which is seen as a different line when viewed
through an instrument called a spectroscope.
Each atom has its own distinct pattern of emission lines
(or bright line spectrum)
and these spectra are used to identify elements
3 Types of Matter
1. Element-
The simplest form of matter that has a
unique set of properties; an element
cannot be broken down into simpler
substances by chemical means.
2. Compound- A substance that contains two or more
elements chemically combined in a fixed
proportion.
Can be separated by chemical means
3. Mixture-
A physical blend of two or more
substances that are not chemically
combined. Can be separated by physical
means.
Substance
Matter that has uniform and definite composition;
also called pure substance
Based on our definitions of element, compound, mixture
and substance, what are the only things
that we can refer to as substances?
ANSWER: ELEMENTS & COMPOUNDS
Based on the distribution of their components, elements
compounds and mixtures can be classified as either
homogeneous or heterogeneous
Homogeneous-a mixture that is uniform in composition;
components are evenly distributed and not easily
distinguished.
Heterogeneous-a mixture that is not uniform in
composition; components are not evenly
distributed throughout the mixture.
Elements
Nickel
Copper
Compounds
Sodium chloride
Aluminum oxide
Mixtures
Soil
Rocky road ice cream
suspension
Vinegar
solution
Based on our definitions and the pictures we saw,
what types of matter are homogenous?
•
•
•
Elements
Compounds
Mixtures-solutions only
Based on our definitions and the pictures we saw,
What types of matter are heterogeneous?
•Mixtures-but not solutions
How do we describe matter and the changes
that matter undergoes?
We describe matter based on its physical and
chemical properties and the physical and chemical
changes that it undergoes.
Physical Property-Those characteristics that can be
observed without the production of a
new substance.
Ex.: color
odor
taste
hardness
density
melting point
boiling point
conductivity
ductile (can be drawn into wires)
malleable (can be hammered into sheets)
luster (shine)
Chemical property- Characteristics that describe how
the substance interacts (or fails
to interact) with other substances
to produce new substances.
Ex.: reactivity
flammability
combustibility
(no longer have the original substance and can’t get it back)
Physical Change- When one or more physical properties
of a substance are changed but
without any change in the substance’s
chemical properties or composition.
Ex.: change of color
grinding of substance
magnetizing of iron
melting
boiling
dissolving
Chemical change- Any change that results in the
production of one or more substances
that differ in chemical properties and
composition form the original substance
Ex. rusting of iron
souring of milk
burning of paper
Law of Conservation of EnergyIn any chemical or physical process, energy is neither
created nor destroyed
Law of Conservation of Matter/Mass
In any physical or chemical reaction, mass is conserved;
mass can be neither created nor destroyed.
Mass of reactants = Mass of products
2H2
4g
+
O2 
32 g
2H2O
36 g
Physical Means of Separation
1. Filtration-a process that separates a solid from
the liquid in a heterogeneous mixture
Chromatography
The separation of mixtures into their constituents by
preferential adsorption
Distillation/Fractional Distillation
A process used to separate dissolved solids from a
liquid, which is boiled to produce a vapor that
is then condensed into a liquid