Download Chapter 5 Atomic Structure & the Periodic Table

Chapter 5 Atomic Structure &
the Periodic Table
5.1 Atoms are the smallest form of
elements.
• 2400 years ago, Greek philosophers believed
everything was made up of air, fire, water, and
earth. Everything else was a mixture of these 4
substances.
• Today, we know there are about 100 basic
substances, known as the elements.
• Sometimes, elements can be found by
themselves. Most often they are found combined
with other elements to make new substances.
Atoms in the Earth & Living Things
• Hydrogen atoms make up about 90% of the
mass of the universe.
Humans
Earth's Crust
12%
23%
47%
28%
Oxygen
Oxygen
Iron
Nitrogen
Silicon
Other
8%
5%
Other
Aluminum
10%
3%
3%
61%
Hydrogen
Carbon
Element Names
• Magnesium = region in Greece known as
Magnesia
• Lithium = Greek word lithos, meaning
stone
• Neptunium = after the planet Neptune
• Hydrogen (H), Sulfur (S), Carbon (C)
• Gold (Au), Lead (Pb), Iron (Fe), Copper
(Cu) = symbols come from latin names.
Dalton’s Atomic Theory
• British scientist, John Dalton, proposed that
each element is made of tiny particles called
atoms.
• All of the atoms in a particular element are
identical but are different from atoms of all other
elements.
• Atoms cannot be divided into anything simpler.
(This was found to be untrue when protons,
neutrons & electrons were discovered).
Structure of Atoms
• Atoms can either be positively or
negatively charged.
• Particles with the same type of charge
repel each other.
• Particles with different charges attract
each other.
• Atoms are composed of protons, neutrons
& electrons.
The Atomic Model
Uncharged;
inside
nucleus
Same Mass
Contains
protons &
neutrons;
positively
charged
Positive
Charge;
inside
nucleus
Negative
charge; move
around outside
nucleus
(electron cloud)
.
Millions of atoms could fit in a space the size of this dot.
It would take you 500 years to count all the atoms in a grain of
salt!!
Relative Sizes
• The electron cloud is about 10,000 times the
size of the nucleus.
• Electrons are MUCH smaller than protons or
neutrons
• Electrons remain evenly spread out in the
electron cloud because they repel each other.
However, they are attracted to the nucleus
because it is positively charged.
• Neutral atoms have no overall electrical charge
because they have an equal number of protons
and electrons.
Atomic Number
• The identity of an atom is determined by
the number of PROTONS in its nucleus.
This is called the ATOMIC NUMBER!
• Hydrogen is atomic number 1. Therefore,
it has one proton in its nucleus.
• How many protons does Lithium have in
its nucleus?
– Nitrogen?
– Gold?
Atomic Mass
• Atomic Mass = the total number of protons
and neutrons in an atom’s nucleus.
• Atoms of a certain element always have
the same number of protons. However,
they don’t always have the same number
of neutrons. Therefore, not all atoms of a
certain element have the same atomic
mass.
Isotopes
• Isotopes are atoms of the same element
that have a different number of neutrons.
• Ex: Chlorine
– All chlorine atoms have 17 protons.
– Some chlorine atoms have 18 neutrons and
some have 20 neutrons. These are chlorine
isotopes.
• Isotopes have different numbers of
neutrons!
How to find the number of neutrons
in a particular isotope.
Atomic Mass – Atomic Number = # of neutrons
# of protons &
neutrons
# of protons
Ions
• An ion is formed when an atom loses or
gains one or more electrons.
• Since the number of electrons in an ion is
different from the number of protons, an
ion does have an overall electric charge.
• See pgs. 142 & 143