Download Physical Science Chapter 16 Notes (Properties of Atoms and the

Physical Science Chapter 16 Notes (Properties of Atoms and the Periodic Table)
SECTION 1 (Structure of the Atom)
1) Atom – the smallest particle of an element that retains the element’s properties.
a) All atoms are composed of protons, neutrons, and electrons.
i) Electron--negatively charged particles surrounding the center of an atom. Electron cloud—is the area around the
nucleus of an atom where the electrons are most likely to be found.
(1) The electron is responsible for most of the interactions between different elements. The mass of the electron is Me =
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2)
3)
4)
5)
9.109 X 10 kg. It takes about 2000 electrons to have the same mass as one proton.
ii) Neutron--neutral particle, composed of two downs and an up quark, inside the nucleus of an atom
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(1) The mass of the neutron is Mn = 1.672 X 10 kg
iii) Proton--positively charged particle composed of two ups and a down quark, inside the nucleus of an atom.
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(1) The mass of the proton is Mp = 1.672 X 10 kg
Quarks – There are six -- up, down, top, bottom, strange & charmed.
The Atomic Model
a) Ancients Greeks thought matter was composed of tiny, indivisible particles called atoms.
i) Four different atoms: fire, water, earth, and air.
b) In 1803 John Dalton developed the first true atomic theory.
i) Believed that atoms may be distinguished by their mass.
ii) Stated that all atoms of the same element have the same mass.
iii) Atoms of different elements have different masses.
c) In 1897 J.J Thompson proved the existence of negatively charged particles within atoms.
i) In a cathode ray tube particles would flow from one electrode to another
ii) Also, the rays would bend toward a positively charged plate, so the ray had to carry a negative charge
iii) Thompson discovered the first subatomic particle, the negatively charged electron
d) In 1911 Ernest Rutherford demonstrated the existence of protons
i) Alpha particles – positively charged particles emitted by certain radioactive materials
ii) Rutherford fired alpha particles at a very thin sheet of gold foil that was surrounded by a screen. The screen would glow
whenever an alpha particle struck it. Rutherford found that three things would happen: some of the alpha particles would
pass straight through the foil, electrons would deflect some, and some would bounce back.
iii) Rutherford deduced that the alpha particles that bounced back were repelled by subatomic, positively charged particles.
These positively charged subatomic particles are called protons.
Even with the discovery of protons scientists knew that there was still some “missing” mass in atoms
a) Example: hydrogen has one proton and one electron, so helium should have just two protons and two electrons. If that were
true, the ratio of the mass of the helium atom to the mass of a hydrogen atom would be 2:1, but experiments showed that the
ratio was actually 4:1.
b) In 1932 James Chadwick conducted experiments similar to Rutherford’s using a sheet of beryllium instead of gold.
c) Unidentified high-energy radiation was given off. Chadwick was able to prove that the radiation was made up of electrically
neutral particles that weighed about as much as protons.
d) These electrically neutral subatomic particles are found in the nucleus of an atom, and are called neutrons.
In the early 1910s, Niels Bohr developed the idea that electrons circled the nucleus of an atom in orbits called orbital.
In 1926 Werner Heisenberg demonstrated that both the motion and the exact position of an electron could never be known
precisely at the same time. As a result, he proposed that there are regions called energy levels where the electrons are most likely
to be.
SECTION 2 (Masses of Atoms)
1) The mass of an atom is measured using relative units called atomic mass units (amu).
a) Protons and neutrons each have about the same mass—nearly 1 amu
2) Mass number –( Atomic mass) is the number of protons and neutrons in an atom.
a) Because electrons have such a small mass they are ignored when calculating the mass of an atom. It takes nearly 2000
electrons to equal the mass of one proton.
3) Atomic Number – the number of protons an atom has in its nucleus.
4) Isotopes – atoms of the same element that have a different number of neutrons
i) Isotopes are indicated by writing the element’s name followed by the mass number
ii) Example: carbon-12 would have six protons and six neutrons, while carbon-13 would have 6 protons and 7 neutrons
Physical Science Chapter 16 Notes (Properties of Atoms and the Periodic Table)
5) Average atomic mass – the average mass of all the isotopes for that element
SECTION 3 (The Periodic Table)
1) In 1869 Russian chemist Dmitri Mendeleev proposed an arrangement of
the known elements based on their atomic mass
atomic
number
state
2) The modern Periodic table differs from Mendeleev’s.
G
8
a) Periodic table--is arranged in order of increasing atomic number
resulting in periodic changes in properties.
symbol
b) In any square of the periodic table you can find the following
Oxygen
information: the symbol for the element, the atomic number, and the
16.00
average atomic mass. Also, some periodic tables will indicate the
state of the element as it is found in nature.
i) Group—(or families) are the vertical columns in the periodic
mass
table.
number
ii) Period—are the horizontal rows of elements on the periodic
table.
3) The electron cloud structure
a) Neutral atom, the number electron equal the number of protons
b) Electrons within the electron cloud have different amounts of energy
c) The differences in energy determines the location of the electrons
d) Energy levels nearer the nucleus have lower energy than those levels that are farther away
e) Energy levels are filled with electrons from the levels closest to the nucleus to the levels farthest from the nucleus
f) Elements in the same group have the same number of electrons in their outer energy level
O
4) Valence Number--is an element's ability to combine with other elements and is determined by the
electrons in the outer most energy level.
a) + 1 Valence--means that the atom becomes positive after giving up and electron.
b) + 2 Valence--means that the atom becomes twice as positive after giving up 2 electrons.
c) +3 Valence--means that the atom becomes three times as positive after giving up 3 electrons.
d) - 1 Valence--means that the atom becomes negative after gaining and electron.
e) - 2 Valence--means that the atom becomes twice as negative after gaining 2 electrons.
f) - 3 Valence--means that the atom becomes three times as negative after gaining 3 electrons.
Physical Science Chapter 16 Notes (Properties of Atoms and the Periodic Table)
QUANTUM MECHANICAL MODEL OF THE ATOM
1. K shell--contains 1 sub-shell (S)
a.
The (S) sub-shell can only contain 2 electrons.
b.
TOTAL OF 2 ELECTRONS IN THIS ENERGY LEVEL
2. L shell--contains 4 sub-shells, 1 (S) sub-shell and 3 (P) sub-shells
a.
(S) sub-shell can only contain 2 electrons
b.
3 (P) sub-shells can contain 2 electrons each. 2 X 3 = 6
c.
TOTAL OF 8 ELECTRONS IN THIS ENERGY LEVEL
3. M shell--contains 9 sub-shells 1 (S), 3 (P), 5 (D)
a.
(S) sub-shell can only contain 2 electrons
b.
3 (P) sub-shells can contain 2 electrons each. 2 X 3 = 6
c.
5 (D) sub-shells can contain 2 electrons each. 2 X 5 = 10
d.
TOTAL OF 18 ELECTRONS IN THIS ENERGY LEVEL
M Shell
L Shell
K Shell
P
N
S
S
P1
P2
P3
S
P1
P2
P3
D1
D2
D4
D5
D3
1 MOLE = 6.022 × 1023 ATOMS
AVOGADRO ' S NUMBER
6.022 × 1023
1 MOLE OF ELEMENT = ATOMIC MASS OF ELEMENT
USES OF MOLAR MASS OF AN ELEMENT
1. TO FIND THE NUMBER OF MOLES OF AN ELEMENT OF A GIVEN MASS
Number of moles = mass
(
1 mol
number of grams
)
2. TO FIND THE NUMBER OF ATOMS OF AN ELEMENT IN A GIVEN MASS
Number of atoms = mass
(
1mol
number of grams
)(
6.022×1023 atoms
1mol
)
3. TO FIND THE MASS OF A GIVEN NUMBER OF MOLES OF A GIVEN ELEMENT
mass = number of moles
(
number of grams
1mol
)