Transcript The Periodic Table

The Atom
An atom consists of a
• Nucleus (protons and neutrons)
• Electrons in space about the nucleus.
Electron cloud
Nucleus
The ATOM
The atom is mostly
empty space
Most of the mass of an atom is in the
nucleus. Protons and neutrons have
a mass of 1.
Atomic mass = # protons + # neutrons
Electrons
Travel around the nucleus in
the electron cloud
which is mostly empty space
• the number of electrons is equal to the number
of protons since elements have no charge.
• Electrons are extremely small. One teaspoon of
water has 3 times as many atoms as the Atlantic
Ocean has teaspoons of water.
ATOM
COMPOSITION:
CHARGES
Protons have a
charge of +1
Electrons have a
charge of -1
Neutrons have NO charge
•Atomic number: number of protons in an atom, =
number of electrons in electron cloud
• Atomic mass: number of protons plus neutrons
• Most common ions
An element has 28 protons
and 31 neutrons: What is
it?
• Nickel: 28 protons, 31 neutrons
• # neutrons =
atomic mass – atomic number
An element has an atomic mass of 184.
How many protons does it have?
How many electrons does it have?
How many neutrons does it have?
Tungsten: Atomic mass = 184
Atomic number = 74
74 protons, 74 electrons
110 neutrons (184 – 74 = 110)
Isotopes
• Atoms of the same element but different
mass number.
• Boron-10 (10B) has 5 p and 5 n
• Boron-11 (11B) has 5 p and 6 n
11B
10B
Isotopes &
Their Uses
Bone scans with
radioactive
technetium-99.
CARBON-14 – RADIOACTIVE ISOTOPE
• Occurs in trace amounts
in the atmosphere
• Absorbed into living
organisms
• The half-life of carbon14 is approx 5700 years
(when half the C-14 is
converted to N-14)
Atomic Symbols for Isotopes: 2 Ways
 Show the name of the element, a hyphen, and the
mass number: sodium-23,
sodium-24
 or show the mass number and atomic number in
symbol form
mass number
23 Na
atomic number
11
Isotopes?
Which of the following represent
isotopes of the same element?
Which element is it?
234
92
1
X
234
235
X
93
238
X
92
2
X
92
3
4
Compounds
• a pure substance composed of 2 or more
elements in a fixed ratio that can be
separated by heat and electricity
• properties differ from those of individual
elements
• Ex : table salt (NaCl)
A MOLECULE is 2 or more NONMETAL atoms bonded
together by COVALENT BONDS– they may be the same element
(ie diatomic molecule) or they may be different elements (ie
caffeine)
Composition of molecules is given
by a MOLECULAR FORMULA
H2O
C8H10N4O2 - caffeine
ELEMENTS THAT EXIST AS
DIATOMIC MOLECULES
Remember:
The “GENS”
These elements
exist as PAIRS
when ALONE.
Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Halogens
(F2, Cl2, Br2, I2)
(P4 and S8)