Transcript Atoms - Edmonds

Atoms
Elements vs. Compounds
 Elements can NOT be chemically broken
down to a simpler substance, compounds
can. (Ex. H2O  H2 + O2)
 Pure substances can be either elements
or compounds. Most materials are
MIXTURES of pure substances.
 There are only 88 naturally occurring
elements, 114 elements that are known.
Dalton’s Atomic Theory
 Elements are made of tiny particles
called ATOMS
 All atoms of a given element are identical
 The atoms of a given element are
different from those of any other element
Atomic Theory Cont’d
 Atoms of one element can combine with atoms
of other elements to form compounds. A given
compound always has the same relative
numbers and types of atoms.
 Atoms are indivisible in chemical processes.
That is, atoms are not created or destroyed in
chemical reactions. A chemical reaction simply
changes the way atoms are grouped together.
Law of Constant
Composition
 A given compound always contains the
same proportions (by mass and by
number) of its elements
 This means a given compound always
has the same composition, regardless of
where it came from.
Chemical Formulas
 A formula describes how a compound is
composed in terms of atoms (how many
and which)
How many of each atom are in:
 Na2CO3
 (NH4)3PO4
ATOMS
Subatomic Particles
 Protons – (p+)
 Defines the element
 Is the integer number (Atomic Number) on the periodic
table
 Have a positive charge
 Has a mass of 1 a.m.u.
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How many protons does Carbon have?
How many protons does Iron have?
How many protons does Ununnilium have?
What element has 35 protons?
Subatomic Particles
 Neutrons – (n0)
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Have no (neutral) charge
Have a mass of ~1 a.m.u.
Contribute to the total mass of an atom
Define the isotope of an atom
 How many neutrons does Carbon-12 have?
 How many neutrons does Carbon 14 have?
 How many neutrons does Uranium-238 have?
Subatomic Particles
 Electrons – (e-)
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Have a negative charge
Equal numbers as protons in NEUTRAL atoms
Gained, lost, or shared in CHEMICAL REACTIONS
Have a mass of 1/1836 th of a proton (neglible!)
How many electrons does Carbon have?
How many electrons does F- have?
Make Up Of Atom
 Protons and Neutrons are in the center of the atom.
 Electrons are whizzing around on the outside of the
atom.
 What element (and isotope) is this atom?
Empty Space
 There is a LOT of empty
space is in between the
nucleus and the
electrons
 If the nucleus was a
marble on the 50 yard
line of a football stadium,
the electrons would be in
the nosebleed seats…
Isotopes
 Isotopes are atoms of an element that
have different masses.
 Same element = same # protons
 Different mass = different # neutrons
 Isotopes are also known as nuclides
 Every element has many nuclides – both
stable and unstable
 The atomic mass on the periodic table is
the weighted average of all the stable
nuclides of that element.
Isotopes
 The specific isotope of any element is written
with the generic formula
AX
Z
Where
Z = the atomic number
A = the mass number (protons + neutrons)
X = the elemental symbol
 Write the symbol for Magnesium with 13
neutrons.
Chart of Nuclides
(black = stable, red = unstable)
Chemical v. Nuclear
Reactions
 Chemical reactions:
 Electrons are involved (exchanged or shared)
 Atoms are rearranged, but stay as the same atom.
 What we will be studying most this year
 Nuclear reactions:
 Nucleii (protons and neutrons) are involved and
changed.
 Atoms become different elements by losing or
gaining protons.