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Chapter 19 Notes: Properties Of Atoms And The Periodic Table
Section 1 page 578 Structure of the Atom
1. There are 117 recognized elements, 92 of which occur in nature, the rest are synthetic
and developed in laboratories. Some of these have existed for only fractions of a second
and are as yet unnamed.
2. Chemical symbols are an abbreviated way to write the name of elements. These may
be a Capital or a Capital followed by a lower case letter. They may be from a Latin
word, or in honor of a scientist, or the location they were discovered, or created in. These
symbols are used worldwide to avoid confusion.
3. An element is matter made up of only one type of atom. An atom is the smallest part
of an element that has the chemical properties of that element. Atoms are made of even
smaller subatomic particles. The three main subatomic particles are:
protons, neutrons, and electrons.
4. Atoms can be divided into two main parts: 1) the positively charged center called the
nucleus, and 2) an electron cloud which surrounds the nucleus.
A. The nucleus contains protons, particles with an electrical charge of 1+, and
neutrons, which are neutral particles with no electrical charge, and no affect on electrical
or chemical properties of an atom, but do help determine the mass.
B. Electrons have an electrical charge of 1-. They are located outside the nucleus
in the electron cloud. The number of negative electrons will always equal the number of
positive protons so the overall charge of an atom is zero.
5. Protons and neutrons are made of arrangements of even smaller subatomic particles
called quarks. A machine called a particle accelerator is used to study quarks. One in
Illinois, is called the Tevatron, SLAC is at Stanford U. in California. They greatly
accelerate charged particles using electric and magnetic fields, and smash them with
protons causing them to break apart into quarks. There are 6 quarks. An arrangement of
3 quarks makes a proton, and 3 different quarks makes a neutron. Electrons are too small
to be made up of anything else.
6. Scientists use models to represent ideas and structures. These models can be scaled
down, or in the case of atoms, made larger. It would take 24,400 atoms to equal the
thickness of an aluminum foil sheet.
7. Timeline of discoveries:
A. 400 BC Greek scientist Democritus proposes all matter is made of atoms. In Greek
atomos means indivisible or uncuttable.
B. 1800s John Dalton, English chemist proposes the Atomic theory:
1. All elements are made of particles called atoms, which can’t be created,
divided or destroyed.
2. Atoms of the same elements have the same size and mass.
3. Atoms of different elements have different sizes and mass.
4. In chemical changes atoms aren’t destroyed, but rearranged.
C. 1904 Joseph Thomson - discovers electrons.
D. 1911 Ernest Rutherford – atoms are neutral, most of the mass is in the nucleus.
E. 1913 Niels Bohr – develops the Bohr model with a central nucleus and electrons
around it in well-defined paths.
F. Current Model – the electron cloud model with a central nucleus and electrons in a
cloud around it.
Read: Section 1 pages578 – 583.
Do: Self-Check page 583 1-5. Using Vocabulary page 602.