3. Objectives
O Describe the structure of matter
O Describe the relationship between
atoms, elements, and molecules
O Identify the symbols of common elements
4.
5.
6. Vocabulary
O Element – made up of all the same kinds
of atoms, each with the same number of
protons and electrons.
O Symbol – one of two letters that represent
the name of the element.
O Molecules – any combination of two of
more atoms that are chemically combined.
7. Elements
O An element cannot be broken down into
simpler substances and still retain all of its
physical properties.
O For example the number 1108 stops being
1108 when you erase any of the four digits.
8. Molecules
O Molecules are combination of atoms that
are chemically changed.
O They may be the same element or the
atoms that combine to form molecules may
be of different elements
O May be 2 atoms or 50, 100, or even 1000
atoms.
9. 17-2 Atomic Particles
O Objectives:
O Identify the atomic particles
O Distinguish between the planetary and the
electron-cloud models of the atom.
10. Parts of the atoms
O Three basic parts:
O The proton
O The electron
O The neutron
11.
12.
13.
14. Vocabulary
O Electron probability cloud – uses regions
instead of fixed orbits of the planetary
model.
O Energy level – the amount of energy of an
electron
O Quantum – the amount of energy an atom
gains or loses
O Quark – a tiny particle that makes up
protons and neutrons.
15. Planetary Model
O Neils Bohr pictured the atoms like a tiny
solar system.
O The protons and neutrons of helium are
packed tightly together in the center of the
atom.
16. Planetary Model
O According to this model, an electron can
orbit the nucleus only at certain distances
from the nucleolus.
O In any given orbit, or energy level, an
electron has a definite amount of energy.
O When an atom gains energy, one of the its
electrons moves to an orbit with a larger
radius.
O An atom releases energy when one of its
electrons moves to a smaller orbit.
17. Atomic Particles
O The amount of energy gained or released equals the
energy difference between the two orbits.
O Scientists say that energy in the atom exist as
units, because it can gain or lose only definite
amounts of energy, or quantum.
O The planetary model of the atom served a purpose
but is now longer adequate because scientists
discovered that electrons did not stay in fixed orbits.
O The electron-cloud model uses electron probability
clouds or regions instead of fixed orbits of the old
planetary model.
O The probability model also predicts which energy
changes are more likely to occur and which ones are
less likely.
18. Atoms
O Quantum ideas are now common in our
everyday language
O Small change in energy a “quantum step”
O Large change in energy a “quantum leap”
19. 17-3 Atomic Number and
Atomic Mass
O Objectives
Distinguish between atomic mass and atomic
number
Explain how atoms of the same element can
differ
Describe how scientists identify isotopes.
21. Atomic Number
O It seems amazing that just the addition or
deletion of a proton can result in such a
major difference.
O The atoms of each element have a
specific number of protons: this number is
the atomic number.
O The number of protons equals the number
of electrons
O This pattern continues until number 109
on the periodic table.
22. Atomic Mass
O Atomic mass equals the number of
protons and neutrons in an atom.
O Atoms of the same element always have
the same number of protons.
O Atoms of the same element that have
different numbers of neutrons are called
isotopes.
O Carbon 12 has 6 protons and six neutrons
O Carbon 14 has 6 protons and eight
neutrons
23.
24. 17-4 The Periodic Table
O Objectives:
O Describe the organizations of periodic table
O Identify the characteristics of
metals, nonmetals, metalloids, noble
gases.
25. The Periodic Table
O Before the year 1500, scientists could identify only
11 of the 109 elements.
O The Bible mentions at least five of these when it
refers to iron, silver, gold, lead and tin.
O Six more elements –
carbon, sulfur, arsenic, antimony, bismuth, and
mercury – were also known.
O Through the centuries scientist added more
elements to the table and today we have either 114
or 118, depending on who you talk to.
O Today, scientists are working to create new
elements.
26. Periodic Table
O During the 1800s enough elements were
known for scientists to start seeing
patterns among them.
O In 1869, a Russian Chemist, Dmitri
Mendeleev recorded the elements in
columns, placing similar elements in a
horizontal row.
O The orderliness of the known elements
became more apparent.
27. The horizontal rows of elements are called periods.
Elements in the same period have electrons in the same
energy levels.
Each vertical column of the periodic table is called a group.
Elements in the same group have similar physical and
chemical properties.
28. Periodic Table
O There are seven periods and eighteen
groups, each labeled with a numeral.
O Each element is give a block on the periodic
table, which contains the chemical symbol for
the element.
O Elements that border the line between metals
and nonmetals are called metalloids.
O These elements sometimes act like metals
and at other times act like nonmetals.
