Download Chapter 3

ATOMS, ELEMENTS,
AND THE PERIODIC
TABLE
Chapter 3
STRUCTURE OF
MATTER
Section 1
1. Structure of Matter
◦ Matter – anything that has mass and takes up space
◦ Anything you can see, smell, touch, taste, even air
◦ Light, emotions, thoughts, ideas are NOT matter
◦ What is matter made of??
Democritus – 460-370 B.C. -> Greek philosopher
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Thought the universe was made of empty space
and tiny bits of stuff
First to describe atoms – Greek “cannot be divided”
Lavoisier – 1743-1794 A.D. -> French Chemist
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Showed that matter does not disappear during
chemical reactions
Law of conservation of matter = matter is not
created or destroyed, only changes form
Models of the Atom
o Scientists use models to …????
Dalton’s Atomic Model
o John Dalton – early 1800s -> English schoolteacher and
chemist
o Designed model known as atomic theory of matter
o Set of ideas: (What kind of model??)
o Matter was made of atoms too small to be seen by
the human eye
o Each type of matter made of only one type of atom
Atoms are extremely small
Models of the Atom, continued
J.J. Thomson – 1856-1940 -> English Scientist
o Used cathode ray tubes
o Observed that rays traveling from the cathode to
the anode could be bent by a magnet
o The rays traveled toward the
positive plate, so the particles
must be negatively charged –
electrons
o Plum pudding or chocolate chip
cookie model – because most
matter is neutral – equal positive
and negative charges
Models of the Atom, cont.
Earnest Rutherford –1909-1910 -> also, Marden & Geiger
o Trying to understand how atom was arranged
o Shot alpha particles at gold foil – alpha particles are tiny and
positively charged
o Most passed through, some were deflected
o Determined that atoms contained a central, positively charged
area – nucleus
o Named the positively charged particles in the nucleus protons
o Suggested that electrons scattered around nucleus
o After the experiment, alpha seemed heavier
o Student named James Chadwick determined they had no
charge and came from the nucleus
o neutrons
Models of the Atom, cont.
o Niels Bohr – 1913 ->student of Rutherford
o Developed new model
o Electrons are arranged around the nucleus in energy levels
o Higher levels are further from nucleus and can contain more
electrons
o Erwin Schrödinger – 1926 –Austrian physicist
o Sub energy levels – nucleus surrounded by electron cloud
o Shows where electrons are more or less likely to be
o Modern physics – protons and neutrons are composed of
smaller particles called quarks – vibrating strings of energy
o Six types: up, down, strange, charmed, top, and bottom
2. The Simplest Matter
◦ Elements
◦ Matter made of only one type of atom
◦ Currently 118 elements, 94 occurring in nature
◦ Synthetic elements are made in nuclear reactor, particle
accelerator, atomic bomb
◦ The Periodic Table
◦ Chart organizing elements by properties
◦ Horizontal rows = periods – elements have same # energy levels
◦ Vertical columns = groups or families – similar bonds and
structural properties
Element Characteristics
Atomic Number – The number of protons in the nucleus
Isotope – atoms of the same element that have different number
of neutrons
Mass number/Atomic mass – the weighted average atomic mass
of all the known isotopes of an element
• Each proton and neutron count as 1 when calculating the
mass number
• The mass of electrons is negligible, and not counted toward
atomic mass
Classification of Elements
3 General Categories - elements within a category have similar
properties
1. Metals – shiny or metallic luster, good conductors of heat
and electricity, malleable, ductile
2. Nonmetals – most are dull in appearance, poor conductors,
many are gases at room temp, bromine is liquid, solids are
brittle
3. Metalloids – have characteristics of metals and nonmetals,
all are solids at room temp, some are shiny, many conductors
(not as good as metals), some used in circuits
3. Compounds and Mixtures
◦ Substance – matter that has the same composition and
properties throughout
◦ May be elements or compounds
◦ Compound – a substance whose smallest unit is made
up of atoms of more than one element bonded
together
◦ Have different properties than the elements that make
them
Compounds have Formulas
o Chemical formula tells you which elements make a
compound as well as how many atoms of each element
are present
Mixture – when two or more substances (elements or compounds)
come together but don’t combine to make a new substance
o Proportions can be changed without changing the identity of
the mixture
o Examples: air, blood, syrup, sand & salt, lemonade
o Can be separated by physical means – dissolving, filtering,
crystallizing, distilling, etc
Mixtures, cont.
o Mixtures can be homogeneous or heterogeneous
o Homogeneous – the same composition throughout
o Can be liquids, solids, or gases
o Can you think of some examples??
o Heterogeneous – the individual substances remain
distinct
o Can you think of some examples??