Date post: | 26-Mar-2015 |
Category: |
Documents |
Upload: | timothy-gunn |
View: | 225 times |
Download: | 0 times |
Summary of the Atom• atoms are the smallest particles that can be uniquely
associated with an element• Atoms cannot break down further by chemical means.• each element has unique atoms • atoms are composed of e-, p and n• atoms are electrically neutral (# of e- = # of p)• for a single element, isotopes differ only in number of
n (neutrons)• atoms have characteristic masses (atomic weights)• atoms combine with one another in definite, whole
number proportions to make compounds
~ 10-10 m
nucleusMass 9 x 10Mass 9 x 10-31-31 kg kg Mass > 10Mass > 10-26-26 kg kg
electron
~ 1 – 7 x 10-15 m (1 – 7 fermi)
atoms are dominantly empty space:
If an oxygen atom had a total radius of 100 km, the nucleus
would be a ~1 m diameter sphere in
the middle.
electron orbits
The Spacious Atom
In a simplistic model, electrons float around the nucleus in energy levels called shells.
As the number of
electrons increases,
they start to fill shells
farther out from the
nucleus.
In most cases,
electrons are lost or
gained only from the
outermost shell.
electron orbits
Electrons in Orbit
AtomAtom
NucleusNucleus
Most of the atom is…
• empty space!
The Nuclear Modelof the atom
• Mass of an electron is approximately 1/1840th of a
proton or neutron.
• Mass of a neutron is very close to the mass of a proton.
• 1 atomic mass unit (amu or u)=
1.66054x10-24g
• 1 g= 6.022 x1023amu• amu is defined by assigning a mass of exactly 12
amu to an atom of C-12 isotope.
1 amu (atomic mass unit) is…
• 1/12th of the mass of one carbon-12 atom.
Most of the mass of the atom is…
• formed by the nucleus.
Subatomic Particles
Particle Symbol Charge RelativeMass(unit)
Electron e- 1- 0
Proton p+ 1+ 1
Neutron n 0 1
Atomic Number, Z (nuclear charge)
11NaAtomic Number
Symbol
is the total number of protons in the atom.
Atoms are identified by their proton numbers.
All atoms of an element have the same number of protons
11
Na
11 protons
Sodium
Number of Electrons
If an atom is neutral ;The net charge on the atom is zeroNumber of protons = Number of electronsAtomic number = Number of electrons in a
neutral atom
Ions• have a net electrical charge since the total
number of electrons isn’t equal to the number of protons.
• can be anions (e->p+ ;formed as a result of gaining electrons; negatively charged), cations (p+>e-;formed as a result of losing electrons; positively charged).
• e- + q(charge of the ion) = proton number
• In chemical rxns, atoms never gain or lose protons. It’s the interaction of electrons.
Mass Number, A (nucleon number)
Counts the number
of
protons and neutrons
in an atom
A= p+ + n0
Protons and neutrons (together) are called “nucleons.”
Atomic Symbols
Show the mass number and atomic number
Give the symbol of the element
23Na
11
(Z)atomic number
(A)mass number
sodium-23
Notation for Atoms
12C13C C
only one isotope of carbon
all isotopes of carbon
only one isotope of carbon
Basic Definitions• “atomic number” = number of protons in the
nucleus;
• “mass number” = sum of protons + neutrons in the nucleus
• “isotopic mass” = mass of a single isotope
More Atomic Symbols
16 31 65
O P Zn
8 15 30
8 p+ 15 p+ 30 p+
8 n 16 n 35 n8 e- 15 e- 30 e-
Learning check
For the ion find
a)Nuclear charge
b)Mass number
c)Electron number
d)Neutron number
23920X
Learning checka) Find the value of unknown quantities in the
table given below.
b) Classify each particle, X, Y, and Z as Cation, Anion and Neutral atom.
Homework!
• Prepare the flash cards having the symbol of the atom on one side and the name on the other side for the first 20 elements on Page 33 in your textbook.
Isotopes
Atoms with the same number of protons,
but different numbers of neutrons.
Atoms of the same element (same atomic
number) with different mass numbers
Isotopes of chlorine
35Cl 37Cl17 17
chlorine - 35 chlorine - 37
Isotopes of Hydrogen element
H
H
H
11
21
31
has the biggest abundance in nature.
Learning Check 1
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30 2) 35 3) 65
B. Number of neutrons in the zinc atom
1) 30 2) 35 3) 65
C. What is the mass number of a zinc isotope
with 37 neutrons?
1) 37 2) 65 3) 67
Solution
An atom of zinc has a mass number of 65.
A. Number of protons in the zinc atom
1) 30
B. Number of neutrons in the zinc atom
2) 35
C. What is the mass number of a zinc isotope
with 37 neutrons?
3) 67
Learning Check 2
Write the atomic symbols for atoms with the following:
A. 8 p+, 8 n, 8 e- ___________
B. 17p+, 20n, 17e- ___________
C. 47p+, 60 n, 47 e- ___________
Solution
16OA. 8 p+, 8 n, 8 e- 8
B. 17p+, 20n, 17e- 37Cl 17
C. 47p+, 60 n, 47 e- 107Ag 47
Learning Check 3
An atom has 14 protons and 20 neutrons.A. Its atomic number is
1) 14 2) 16 3) 34
B. Its mass number is1) 14 2) 16 3) 34
C. The element is1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) 34X 2) 34X 3) 36X 16 14 14
Solution
An atom has 14 protons and 20 neutrons.A. It has atomic number
1) 14
B. It has a mass number of3) 34
C. The element is1) Si
D. Another isotope of this element would be
3) 36X 14