chemical foundations: elements, atoms and...
TRANSCRIPT
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Chemical Foundations:
Elements, Atoms and Ions
Lectures 3, 4, 5
Chem 101
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112 elements are known
88* elements are found in nature; on earth, in the
oceans and atmosphere The most abundant elements
Element Mass Percent Oxygen 49.2
Silicon 25.7
Aluminum 7.50
Iron 4.71
Calcium 3.39
Sodium 2.63
Potassium 2.40
Magnesium 1.93
Hydrogen 0.87
Titanium 0.58
Chlorine 0.19
Phosphorus 0.11
Manganese 0.09
Carbon 0.08
Sulfur 0.06
Barium 0.04
Nitrogen 0.03
Fluorine 0.03
All others 0.49
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Elements of Life
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Some elements are used in their compound
forms rather than as a pure element
Hmco Photo File
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Compare the Earth’s Crust to the
Human Body
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Footprints in the sand
of the Namib Desert in Namibia.
Getty Images (Royalty Free)
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Dalton’s Atomic Theory
• Elements are composed of tiny particles
called atoms.
– All atoms of a given element are identical. – All carbon atoms have the same chemical and physical
properties.
– Atoms of a given element are different from
those of any other element. – Carbon atoms have different chemical and physical
properties than sulfur atoms.
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Elements
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Dalton pictured compounds as collections of atoms.
NO, NO2, and N2O are represented here.
Atoms of different elements combine to
form compounds.
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Dalton’s Atomic Theory
• Law of Constant Composition: – all samples of a compound contain the same
proportions (by mass) of the elements that form the compound.
• Atoms are indivisible by chemical processes. – All atoms present at beginning are present at the
end.
– Atoms are not created or destroyed, just rearranged in chemical reactions.
– Atoms of one element cannot change into atoms of another element.
• Cannot turn lead into gold by a chemical reaction
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Formulas of Compounds
• NaCl Each element is represented by its 1 or 2 letter symbol.
• H2O The number of each type of atom is indicated by a subscript written to the right of the element symbol. If only one atom is present, do not include a subscript.
• Mg(NO3)2 If polyatomic groups are present in the molecule, they are written inside parentheses if more than one group is present.
• KNO3 If only 1 polyatomic group, no parentheses
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Rutherford’s Nuclear Model • The atom contains a tiny
dense center called the nucleus.
– The volume is about 1/10 trillionth the volume of the atom.
• The nucleus is essentially the entire mass of the atom.
• The nucleus is positively charged.
– The amount of positive charge of the nucleus balances the negative charge of the electrons.
• The electrons move around in the empty space of the atom surrounding the nucleus.
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The Modern Atom • Atoms are composed of three
main pieces: protons, neutrons,
and electrons.
• The nucleus contains protons and
neutrons.
• The electrons move around the
space outside the nucleus.
• The protons have a charge of +1
• The neutrons have a charge of 0
• The electrons have a charge of -1
Lithium Atom
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The Elements
Classified as Metals and as Nonmetals.
Elements are arranged in a pattern
called the periodic table
Position on the table allows us to
predict properties of the element
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Elements • Metals
– Lustrous, malleable,
ductile, conduct heat and
electricity
• Nonmetals – Dull, brittle, insulators
• Metalloids – Also called semi-metals
– Some properties of both metals & nonmetals
Gold Au
Platinum Pt
Sulfur S
Boron
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Elements on the Modern Periodic Table
The A columns
are Main Group
Elements or
Families
Elements with
similar chemical
and physical
properties are in
the same column
Transition elements
Inner transition
elements
Rare earth
Periods are rows
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Natural States of Elements
• Gases:
– monoatomic gases such as noble gases
– diatomic gases such as O2
• Liquids such as Hg or Br2
• Solids such as metals or carbon or sulfur S8
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Because these elements all show similar chemical behavior,
they are listed vertically in the periodic table, as a "family" of
elements.
Halogens
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All the elemental forms of the Group 7
elements contain diatomic molecules.
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The noble gases: Group 8 of the periodic
table.
Non reactive
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Argon gas consists
of a collection of separate argon atoms.
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Gaseous nitrogen and oxygen contain
diatomic (two-atom) molecules.
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The decomposition of 2 water molecules (H2O) to form two
hydrogen molecules (H2) and an oxygen molecule (O2)
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Graphite and diamond,
two forms of carbon.
Fundamental Photographs
Some elements can
exist in different
elemental structures.
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The three solid
elemental forms of carbon (allotropes):
(a) diamond, (b) graphite, and (c) buckminsterfullerene.
C60
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Neutral sodium atom (Na).
There are 11
protons in the
nucleus for a
charge of 11+
The number of
neutrons in the
nucleus does not
affect the charge
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Neutral sodium atom
(Na) and sodium ion (Na+).
What noble gas has 10 electrons?
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Neutral magnesium atom
(Mg) and magnesium ion (Mg2+).
What noble gas has 10 electrons?
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Neutral aluminum atom
(Al) and aluminum ion (Al3+).
What noble gas has 10 electrons?
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Atomic Structures of Ions: Cations
• Metals form cations.
• For each positive charge the ion has 1
less electron than the neutral atom. – Na = 11 e-, Na+ = 10 e-
– Ca = 20 e-, Ca+2 = 18 e-
• Cations are named the same as the
metal
sodium Na Na+ + 1e- sodium ion
calcium Ca Ca+2 + 2e- calcium ion
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Neutral chlorine atom
(Cl) and chloride ion (Cl-).
What noble gas has 18 electrons?
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Atomic Structures of Ions: Anions
• Nonmetals form anions.
• For each negative charge the ion has 1
more electron than the neutral atom. – F = 9 e-, F- = 10 e-
– P = 15 e-, P3- = 18 e-
• Anions are named by changing the
ending
of the name to -ide – Fluorine F + 1e- F- fluoride ion
– Oxygen O + 2e- O2- oxide ion
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Ions • Cations: ions that have a positive charge
– Form when an atom loses electrons
• Anions: ions that have a negative charge
– Form when an atom gains electrons
• Ions with opposite charges attract
– Cations and anions attract each other
• Compounds must have no total charge,
balance the numbers of cations and anions in a
compound to get 0 total charge.
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Ionic Charges and Compounds Charges on the ions of some
elements can be predicted from
the periodic table.
Cations and anions usually form
simultaneously to form ionic compounds
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Solid sodium chloride
highly magnified.
Color-Pic, Inc.
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Sodium metal (left) and chlorine gas.
Hmco Photo File.
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The arrangement of sodium ions (Na+) and chloride ions
(Cl-) in the ionic compound sodium chloride.
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When ionic substances dissolve in
water they conduct electricity.
Moving ions conduct electricity.
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NaCl:
Each sodium ion has a 1+ charge
Each chloride ion has a 1- charge,
They must occur in equal numbers to give a net charge of zero.
Formula of Ionic Compounds
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MgCl2: To balance the 2+ charge on Mg2+, two
Cl- ions are necessary to give a net charge of zero.
Formula of Ionic Compounds
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Isotopes
• All atoms of an element have the same
number of protons.
• The number of protons in an atom of a given
element is the same as the atomic number.
– Found on the periodic table
• Atoms of an element with different numbers of
neutrons are called isotopes.
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Two isotopes of sodium.
23Na 24Na
18Na to 35Na
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Isotopes • All isotopes of an element are chemically identical.
– Undergo the exact same chemical reactions
• Isotopes of an element have different masses.
• Isotopes are identified by their mass numbers.
– Mass number = # protons + # neutrons
• How are isotopes formed? – Isotopes are either primordial, or are formed via the decay of heavier
mass radioactive elements. for example, U235 and U238 mined from the earth are primordial (formed in supernova explosions over the course of the billions of years before earth coalesced). They can also be synthesized in the atmosphere and in reactor or accelerator facilities, by processes such as fusion and fission.