Download I. Atoms are the smallest forms

I. Atoms are the smallest forms
– All matter is made of atoms
• Chemists know about 100 basic elements
– Some exist individually
– Some combine to make new substances
– Atoms in Earth’s crust and living things
• 90% of the universe is composed of Hydrogen (H)
– H makes up 1% of the Earth’s crust
– Most are combined with Oxygen (O) in the form of water
I. Atoms are the smallest forms
• Most living things contain 25 types of atoms.
• Most made of four types of atoms
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Oxygen (O)
Carbon (C)
Hydrogen (H)
Nitrogen (N)
– Names and Symbols of Elements
• Each element has a unique name and symbol
– Some use the first letter of their name
– Others have the first letter plus one other.
• If there is one letter to represent, it will always be capitalized
• If two letters, second one is always lower cased.
• Many names derived from Latin, Greek or other names.
I. Atoms are the smallest forms
– Each element is made of different atoms
• John Dalton thought that each element was made
of tiny particles called atoms.
• He stated that each atom of the same type is
identical. Atoms of different kinds do not resemble
any other type.
• Later discoveries indicated that the atom was
broken down in to even smaller parts.
I. Atoms are the smallest forms
– Structure of an atom
• Atoms are composed of three types of particles
• Two are located within the center of the atom
called the nucleus.
– Proton-positively charged particle
– Neutron- neutral particle
– Neutral particles are necessary to prevent all the “+”
charges from repelling each other and causing the
nucleus to become unstable.
– Outside the nucleus are electrons- negatively charged
particles
I. Atoms are the smallest forms
• Electrons are much smaller in size than protons or
neutrons.
• Electrons move so quickly around the nucleus that
they create a cloud around the nucleus.
• Electrons are attracted to the nucleus because of
their negative charge and the protons positive
charge inside the nucleus
I. Atoms are the smallest forms
– Atomic numbers
• Atoms are determined by the number of protons in
the nucleus.
• This creates the atomic number
– Atomic Mass numbers
• The total of the protons and neutrons together give
the atom’s atomic mass number.
I. Atoms are the smallest forms
• Not all atoms of an element have the same atomic
mass
– Atom will have the same number of protons
– But not the same number of neutrons
• This creates an Isotope
– Atoms of the same element that have different number of
neutrons
– Some elements have many isotopes, others have just a
few.
• Isotopes are designated by the name of the
element and the total number of its protons and
neutrons.
• You can find number of neutrons by subtracting
atomic number from Atomic Mass Unit.
I. Atoms are the smallest forms
– Atoms Form Ions
• An atom has the same number of protons and
electrons.
• Each positive charge cancels out a negative
charge.
• There will be no overall charge
• An Ion is formed when an atom gains or loses an
electrons
– When electrons are lost, there are more protons giving
an overall positive charge
– If electrons are gained, there are more electrons giving
an overall negative charge.
I. Atoms are the smallest forms
• Formation of Positive ions
– When electrons lost, less repulsion of remaining
electrons
– Positive ion is smaller than the neutral atom
– Represent an ion using the chemical symbol and how
many electrons have been lost.
– Write as a superscript Ca+2
I. Atoms are the smallest forms
• Formation of Negative Ions
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When electrons gained, more are now there
Negative ion is larger then neutral atom
Extra electrons cause expanding of electron cloud
Represent using the chemical symbol with a negative
subscript and number gained
– Cl– O2-
II. Elements make up the periodic
table
– Elements can be organized by similarities
• One way is by mass of atoms
• Atomic mass of atoms is the average mass of all
the element’s isotopes
– Mendeleev’s Periodic Table
• Organized elements based on properties
• Based on physical and chemical similarities.
• Created the periodic table where the rows
increased in atomic mass
– Predicting New Elements
• Mendeleev left spaces where nothing known fit
• Predicted new elements would complete the chart
II. Elements make up the periodic
table
– Periodic table
• Modern table has elements with similar properties
in columns
• Elements arranged by atomic number, not by
atomic mass
– Reading Periodic Table
• Each square tells specific information
• Top number is the Atomic Number
– Number of Protons
– Located in nucleus
II. Elements make up the periodic
table
• Chemical symbol in the Middle
– is the abbreviation of the element’s name
– Contains one or two letters
– Some are three letters b/c they are not yet named
• The element’s name. Written below symbol
• Atomic mass. Number below name. Atomic mass
is all the isotopes of the element.
II. Elements make up the periodic
table
• Element’s color indicates existence at room
temperature.
– White means gas
– Blue means liquid
– Black means solid
• Background color indicates type of metal
– Metal
– Non metal
– Metalloid
II. Elements make up the periodic
table
– Groups and Periods
• Elements arranged in a column
– Called a group
– Labeled at the top of the column
– Sometimes called a family
• Horizontal rows
– called Periods
– Properties of elements change predictably from one end
to the other.
II. Elements make up the periodic
table
– Trends in Periodic Table
• Atoms on left side of table form positive ions easily
(give away electrons for an overall positive charge)
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Group 1 lose an electron to become +1 Ions
Group 2 loses two electrons to become +2 ions
Group 18 do not form ions at all
Group 17 gain an electron to become negative ions
Group 16 can gain 2 electrons to become -2 ions
Groups 3 to 12 all form positive ions but the charge can
vary
II. Elements make up the periodic
table
• Sizes of atoms vary across periods within groups.
Important because it affects how the atom will
react with another atom
• Densities follow a pattern
– Generally increase from top to bottom
– Elements within a period the left and right sides are least
dense,
• Middle is most dense
III. Periodic table is a map of the
elements
– Distinct regions on the periodic table
• Three main regions
– Metals on the left
– Non metals on the right (except for Hydrogen)
– Metalloids in the middle.
» Yellow box will indicate metal
» Green nonmetal
» Purple metalloid
• Location also indicate reactivity
– Groups 1 and 17 most reactive
– 18 least because they are stable.
III. Periodic table is a map of the
elements
– Most Elements are metals
• Conduct electricity and heat
• Have a shiny appearance
• Easily shaped (malleable) into
– Wire,
– Sheets
– Bent
• Exception is mercury , but all others a solids at
room temperature
III. Periodic table is a map of the
elements
– Reactive Metals
• Group 1
– Called alkali metals
– Very reactive
» Potassium
» sodium
• Group 2 are alkaline earth metals
– Less reactive than alkali
– More reactive then most.
» Calcium
» magnesium
III. Periodic table is a map of the
elements
• Transition Metals
– Groups 3-12
– Generally less reactive
– Found in foods we eat
» Copper,
» Gold
» Silver
» Iron
• Rare Earth Metals
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Located in top row of the two rows of metals
Referred to as Lanthanides
Called this because were once rare
Now only hard to isolate
III. Periodic table is a map of the
elements
– Nonmetals and metalloids
• Elements on right side are the nonmetals
– Opposite properties of metals
– Mostly gasses
» Air is made of nonmetals
» Carbon in living things
• Halogens
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Elements in group 17
Means forming salts
Very reactive
Used to kill harmful microorganisms
III. Periodic table is a map of the
elements
• Noble gasses
– Group 18
– Inert or unreactive
• Metalloids
– Elements having both metal and nonmetal properties.
– Located on either side of the zigzag of table
III. Periodic table is a map of the
elements
– Atoms changing identity
• Chemical reactions do not effect the nucleus of an
atom
• Certain conditions can change the number of
protons
• Each atom has isotopes with different numbers of
neutrons
• Stability of nucleus depends on the right number of
protons and neutrons
• Too few or too many neutrons, nucleus becomes
unstable
• When this happens particles are produced from
the nucleus to restore balance
III. Periodic table is a map of the
elements
• This change is accompanied by a release of
energy
– Marie Curie named this process radioactivity.
– She was first person to isolate polonium and radium
• Isotope is radioactive if nucleus has too many or
too few neutrons
– Rare for small atoms
– Heaviest elements (beyond bismuth, al isotopes are
radioactive
III. Periodic table is a map of the
elements
• Measure radioactivity with Geiger counter
– Detects particles from the breakup of the atomic nucleus
with clicks
– More clicks more particles being produced
– Uses of Radioactivity in Medicine
• Used to destroy tumors
• Monitor activity of certain organs in body
• Large/prolong exposure can do damage.