Elements and Symbols

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Elements and Symbols

• Elements
• 114 are known, 91 occur naturally and the
  others are artificially made in laboratories.
• Are the primary substances of matter
• Are made up of atoms which cannot be broken down
  into simpler substances.
• Atom is the smallest part of an element that
  retains the chemical characteristics.
• Are arranged in the periodic table in order of
  increasing atomic number (Z, number of protons)
• Chemical Symbols
• One or two letter abbreviations, first letter is
  capitalized and the second is lowercase.
• Ca calcium, Co cobalt, C carbon, Fe iron
• S sulfur

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ELEMENTS

• Essential for humans
• O, C, H,N, Ca,P,Mg, K, S, Na, Cl, Zn Fe
• Trace elements Cr, Co, I, Mn Cu.
• Cr metabolism of sugars
• Co present in vitamin B12
• Iodine--- thyroid gland
• Mn maintains proper calcium levels in bones
• Cu involved in production of red blood cells
• Human behavior
• Li ---manic-depressive syndrome
• Codegree of violence

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The Periodic Table

• 7 Periods---horizontal row of elements
• 8 A Groups and 8B Groups---vertical columns
  contain elements with similar properties.
• A groups are called the representative elements
  or the main group elements, and contain metals,
  nonmetals and metalloids.
• B groups are the transition metals
• Bottom rows Inner Transition Elements Rare
  Earth Elements
• Metals (really belong in Period 6 7)

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METALS

• solids at room temperature, except Hg
• reflective surface
• shiny
• conduct heat
• conduct electricity
• malleable
• can be shaped (hammered) into a flat sheet
• ductile
• drawn or pulled into wires
• lose electrons and form cations in reactions
• about 75 of the elements are metals
• lower left on the table, or left of the zig-zag
  line
• Melt at higher temperatures than nonmetals

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NONMETALS

• found in all 3 states
• poor conductors of heat and electricity
• Low melting points and low densities
• solids are brittle, and dull
• Good insulators
• gain electrons in reactions to become anions
• upper right on the table
• except H

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METALLOIDS

• show some properties of metals and some of
  nonmetals
• also known as semiconductors, and insulators
• Better conductors than nonmetals but not as good
  as metals
• B, Si, Ge, As, Sb, Te, Po, At.

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IA, Alkali Metals IIA, Alkali Earth Metals

• soft, low melting points,low density
• very reactive, never find uncombined in nature
• tend to form water soluble compounds

• harder, higher melting, and denser than alkali
  metals
• reactive, but less than corresponding alkali
  metal
• form stable, insoluble oxides

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VIIA, Halogens VIIIA, Noble Gases

• nonmetals
• F2 Cl2 gases
• Br2 liquid
• I2 solid
• all diatomic
• very reactive

• all gases at room temperature,
• very low melting and boiling points
• very unreactive, practically inert
• very hard to remove electron from or give an
  electron to

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Natural States of the elements

• Do NOT exist in nature in pure form, uncombined
• exist as compounds, (elements combined with other
  elements) and also as mixtures.
• Pure form (elemental) Au, Ag, Pt and noble gases
  of group 8A.
• Allotropesdifferent forms of the same element
• Carbon graphite, diamond, C60

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Daltons Atomic Theory

• 1. All matter is made up of tiny particles called
  atoms
• 2. All atoms of a given element are similar to
  one another but different from atoms of other
  elements
• 3. Atoms of two or more different elements
  combine to form compounds
• 4. In chemical reactions, atoms are indivisible
  (not broken or changed into another type). Atoms
  are not created or destroyed, just rearranged
• therefore the total mass will remain the same
• Law of Conservation of Mass

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SIZES OF ATOMS

• Relative masses of the atoms are based on
• C-12 12 amu exactly
• unit atomic mass unit
• 1amu 1/12 of mass of C-12 1.6606 x 10-24 g
• amu or dalton
• absolute sizes of atoms
• mass of H atom 1.67 x 10-24g
• volume of H atom 2.1 x 10-25cm3

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STRUCTURE OF THE ATOM

• J.J. Thomson discovered the electrons (negative
  particles) in late 1890
• William Thomson (Lord Kelvin)plum pudding model
  of the atom
• 1911 Ernest Rutherford --- atom has a dense
  center of positive charge (nucleus) around which
  electrons move in an empty space. Nucleus is made
  up of protons which have same magnitude charge as
  the electron but positive.
• 1932 James Chadwick discovered the neutrons.

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The Modern Atom

• We know atoms are composed of three main pieces -
  protons, neutrons and electrons
• The nucleus contains protons and neutrons
• Atoms have different chemical properties because
• Arrangement of electrons
• Valence electrons

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ATOMIC NUMBER, ZMASS NUMBER A and ISOTOPES

• Atomic Number, Z, number of protons
• Mass Number, A, protons neutrons
• Whole number
• Abundance relative amount found in a sample
• Isotopes have the same Z, same number of protons
  but different mass number A, different number of
  neutrons.
• C-12, C-13, C-14

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ISOTOPES

• Ratio of isotopes found in animals and humans
  reflect their diets (13C/12C, 15N/14N)
• Radiocarbon dating or carbon-14 dating
• Method used for dating ancient articles made from
  wood or cloth
• Decays by beta particles.

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ISOTOPES

• Radiotracers are radioactive nuclide
• I-131 thyroid
• Fe-59 Cr-51 red blood cells
• Mo-99 metabolism
• P-32 eyes, liver, tumors
• Sr-87 bones
• Tc-99 heart, bones, liver, lungs
• Xe-133 lungs
• Na-24 circulatory system
• Ta-201 heart muscle

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Mass Number is Not the Sameas Atomic Mass

• the atomic mass is an experimental number, is the
  average of the mass of all naturally occurring
  isotopes are not always whole numbers.
• the mass number refers to the number of protons
  neutrons in one isotope
• natural or man-made

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PROBLEM

• Naturally occurring carbon consists of three
  isotopes, 12C, 13C, and 14C. State the number of
  protons, neutrons, and electrons in each of the
  following.
• 12C 13C 14C
• 6 6 6
• protons ______ ______ ______
  
• neutrons ______ ______ ______
  
• electrons ______ ______ ______
  

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PROBLEM

• Write the nuclear symbols for atoms with the
  following subatomic particles.
• A. 8 p, 8 n, 8 e- ___________
• B. 17p, 20n, 17e- ___________
• C. 47p, 60 n, 47 e- ___________

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Atomic Mass Problem

• Rubidium has two naturally occurring isotopes
  one has a mass of 84.9118 amu and a natural
  abundance of 0.7217 and the other a mass of
  86.9092 amu and the abundance of 0.2783.
  Calculate the average atomic mass of Rubidium.
• Atomic mass of Rb (84.9118 amu x 0.7217)
  (86.9092 amu x 0.2783) 85.47 amu

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IONS

• Atoms acquire a charge by gaining or losing
  electrons
• not protons!!
• Ion Charge protons electrons
• ions with a charge are called cations
• more protons than electrons
• form by losing electrons
• ions with a charge are called anions
• more electrons than protons
• form by gaining electrons

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CATIONS The Periodic Table

• For the main group metals the charge is equal to
  the group number
• Na ? Na 1e- (1A) sodium ion or
  cation
• 11p 11p
• 11e- 10 e-
• The size of the cation is smaller than the size
  of the neutral atom
• Ca ? Ca2 2e- (group 2A) calcium ion
• 20p 20p
• 20e- 18-

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CATIONS of Transition Metals

• They form cations with various charges
• Cu or Cu2 copper (I) ion copper(II)
  ion
• Fe2 or Fe3 iron(II) ion ion (III) ion

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IONIC COMPOUNDS

• Are made when a metal combines with a nonmetal,
  or a cation with an anion
• Are NEUTRAL, the charge on the cation has to
  cancel the charge on the anion
• In aqueous solution or molten they conduct
  electricity because the ions are mobile (ions can
  move)
• In solid form they do not conduct electricity
• Mg2 O2- MgO Ca2 P3- Ca3P2

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ANIONS The Periodic Table

• The charge for the nonmetal is calculated
• group number -8
• VA charge is 5 8 -3
• VIA charge is 6 8 -2
• VII A charge is 7 8 -1
• The size of an anion is larger than the size of a
  neutral atom
• O 2e- ? O 2- F 1e- ? F-
• oxide ion fluoride ion