Transcript Ch 3 PowerPoint

Ch 3 Atoms and Periodic
Table Notes
Vocab: nucleus, proton, neutron, electron, Energy
level, orbital, Valence electron, Periodic law, Period,
Group, Ionization, Ion, Cation, Anion, Atomic number,
Atomic mass number, Isotopes, Atomic mass unit,
Average atomic mass, Metals, Nonmetals,
Semiconductors, Alkali metals, Alkaline-earth metals,
Transition metals, Halogens, Noble gases
3.1 Atomic Structure
What gives different matter distinct
properties?
- the atoms in that type of matter
Atoms are tiny units that determine
properties of matter
- each element has its own atom
Dalton’s Atomic Theory – 1808
English schoolteacher
• Every element is made of tiny particles
called atoms that can’t be divided.
• Atoms of the same element are exactly
alike.
• Atoms of different elements can join to
form molecules.
- We have since learned that atoms can be
divided.
Atomic Structure
Nucleus = center of atom
• Protons + neutrons
• Overall positive charge
Electron Cloud = surrounds nucleus
• Contains space where electrons are found
• Overall negative charge
Overall positive and negative attraction
keeps electron cloud close to the Nucleus
Sub-Atomic Particles
Proton = “+” charged molecule in nucleus
• Written as “p+”
• Mass of 1.67 x 10-27
Neutron = a neutral particle in nucleus (NO
charge)
• Written as “n”
• Mass of 1.67 x 10-27
Electron = a “-“ charged particle moving
around the outside of nucleus in an
electron cloud… think of fan blades
• Written as “e-“
• Mass of 9.11 x 10-31…. Very little mass
Atoms have no overall charge because they
have an equal number of protons and
electrons.
Electron Cloud Orbitals
It is impossible to know the exact location of
a given electron in its electron cloud.
So… we have a general area based on an
electron’s energy level. General rule = the
more energy an electron has, the farther
from the nucleus and the positive protons
it can get.
Orbitals = a region in an atom where there is
a high probability of finding electrons; we
only look at two types, there are more.
• S-orbitals are spherically shaped
– Holds first two electrons of every element
– Is the lowest energy level
– After 1st S-orbital is full, a second fills with 2
more e-
• P-orbitals are peanut shaped
– When the 2 s-orbitals are full (4e-), the 5th
through 10th electrons will fill p-orbitals
– These electrons have slightly more energy
than the first 4
Electron Clouds and Energy
Electrons move about the electron clouds
(orbitals) based on their energy levels.
Analogy: sun and planets
• General Atomic Model
• 1st energy level
– s-orbital with 2e-
• 2nd energy level
– s-orbital with 2e– 3 p-orbitals with 2e- each = 6e-
Valence electron = an electron in the outermost
energy level of an atom
• hydrogen has 1; helium has 2; lithium has 1
• these are the electrons that will allow the
atom to react with others
3-2 A Guided Tour of the Periodic
Table
The periodic table is a visual representation
of the elements organized by
properties.
• Each element has a symbol
• Organized by # of protons; also called the
atomic number
• Periodic law = properties of elements tend
to change in a regular pattern when
elements are arranged in order of
increasing atomic number, or number of
protons in their atoms.
History of the periodic table
Dmitri Mendeleev (18341907)
• Organized 70 known
elements into a able
according to common
characteristics.
• Problem  there were
many empty spaces and it
was very long
Henry Moseley (1887-1915)
• Determined the atomic number of
elements and recognized Mendeleev’s
table to what we know today
The Periodic Table
Periods are horizontal rows
• There are 7 periods
• The # protons and electrons increases
from left to right
• Other properties also follow pattern
including size of molecule
Groups are vertical columns
• Also called families because elements in
the same group share physical and
chemical properties.
• Elements in a group have the same # of
valence electrons
• Each group is identified by a number and
letter
Ions
Atoms that do not have a filled outermost
energy level may undergo a process
called ionization.
The atom will either gain or lose valence
electrons.
Example: Element Lithium from Group 1 is
very reactive. Li will give away its 3rd
electron and become a positive ion.
All elements in the first group on the periodic
table will react the same way
• A positive ion is called a cation
• A negative ion is called an anion
Each element and its information can be
found in a box on the periodic table.
• General format:
Atomic number
• Is equal to the number of protons in the
nucleus
• Will also equal the number of electrons in
the electron cloud
• Will always be a whole number on the
table (no decimals)
Atomic mass
• The mass of the nucleus of the atom
• The combined number of protons AND
neutrons in an atom
• Atomic mass = p + n
• Will always be the larger number
8
Oxygen
16
12
Carbon
6
• Protons =
• Electrons =
• Neutrons =
• Protons =
• Electrons =
• Neutrons =
4
Helium
2
5
Boron
11
• Protons =
• Electrons =
• Neutrons =
• Protons =
• Electrons =
• Neutrons =
Isotopes
• Different versions of an element that have
different numbers of neutrons.
• They have the same # protons, but
different masses
• This is why the average atomic masses on
the periodic tables are decimals, the mass
is a combination of all isotopes.
– Ex: Hydrogen has 1p+, 1e-, and has a mass
of 1.007 because it is mostly found as an
isotope with no neutron
The mass of an atom
• It is very small, so they decided to
measure a Carbon-12 atom (6 protons and
6 neutrons) and divide into 12… meaning
they said each proton and neutron equals
1 atomic mass unit
3-3 Families of Elements
- How are elements classified?
• Metals versus Nonmetals
• Most elements are metals
– Most metals are shiny solids that can be
stretched and shaped
– They are good conductors of heat and
electricity
• Nonmetals are usually on the right of the
periodic table
– Include solids, liquids and gases
– Nonmetal solids are usually poor conductors
of heat and electricity
– Some can conduct under certain conditions –
semiconductors
The Periodic Table
• Metals – There are 4 different groups
Alkali Metals - Group 1 (except
hydrogen)
• Soft and shiny
• Have one valence electron; forms
cations very easily
• React violently with water; elements are
usually stored in oil
• Only found in compounds in nature
video
Alkaline Earth Metals – Group 2
•
•
•
•
Have 2 valence electrons
May react to form ions with +2 charge
Calcium is very important in skeletons
Magnesium is the lightest structural
material
Transition Metals – Groups 3-12
• May lose electrons to form multiple cations
• All conduct heat and electricity
– Copper wire
• Can be stretched and shaped without
breaking; gold and silver jewelry
Synthetic Elements
• Some of the transition metals are manmade – Tc-43, Pm-61 and Atomic numbers
93 and above
• Many are radioactive… the nuclei are
continually decaying to produce different
elements
Nonmetals – all but Hydrogen are
found on the right of P. Table
Carbon is a very important non-metal
• Pure state – graphite, pencil lead
• Diamond
• In body structure
Halogens – Group 17
• Very reactive; gain electron to form -1
anions
• Chlorine is used to kill bacteria – pools,
drinking water
• Fluorine anion prevents tooth decay
Nobel Gases – Group 18
• Exist as single atoms because they
are inert or unreactive… the outer
energy level is full of electrons
• Neon is used in “neon” signs
• Helium is less dense than air… it
floats
Semiconductors or metalloids – 6
elements
• Have some properties of metals
• Under certain conditions, they can conduct
heat and electricity
• Silicon is very important in modern
technology