WHAT ARE ATOMS?
What are Atoms?
■ Atoms- The smallest particles of an
element that have the same
chemical properties as the element.
■ The atoms of one element are
different from the atoms of another
element.
■ Each element is made up of a
particular type of atom and has its
own special properties.
■ Atoms are so small that billions of
atoms fit on the head of a pin.
The Parts of an Atom
■ Nucleus- the densest part of the atom, where most
of its mass is. The rest of the atom is just empty
space.
■ Inside the nucleus are:
– Protons- have a positive electric charge
– Neutrons- have no electric charge.
■ The atomic mass (amu) is the sum of the atoms
protons and neutrons.
■ Electrons-have a negative electric charge.
– They are smaller than protons and they circle
around the nucleus.
– They are held near the nucleus by an
attraction to the protons.
■ An atom has equal numbers of protons, neutrons,
and electrons
How Have Ideas About Atoms Changed?
■ 1803- John Dalton proposed that atoms were solid like
marbles and had no particles inside.
■ 1898- J.J. Thompson showed that atoms contained
electrons. He proposed that electrons were sprinkled in
positively charged fluid.
■ 1913- Earnest Rutherford and H.G.J Moseley showed that
positive matter in atoms was packed into a tiny nucleus.
■ 1926- Scientists have thought of electrons as “clouds”
surrounding the nucleus.
Elements
All things around us are made with just a few kinds of matter.
Each kind of matter has its own set of properties.
■ There are over 100 basic kinds of matter called
elements.
– Elements are the basic building block of
matter.
– They combine to make up all other kinds
of matter.
– They cannot be broken into smaller pieces
with ordinary physical or chemical
processes.
More than 75% of the elements are called metals. Metals
are shiny, bendable, and able to conduct heat energy and
electricity well.
Periodic Table
of Elements
• This contains all of the known elements.
• Elements can be combined to make
other things
• For example, hydrogen and oxygen
combine to make water.
Element properties
■ Each element has its own set of chemical and physical properties
– Chemical properties describe how a material changes into other materials
– Physical properties can be measured without changing the material
■
Examples: color, odor, mass, volume, Density, texture, Magnetism and hardness.
■
These properties do not change.
What is the Periodic Table?
■ 1868- Dmitry Mendeleyev tried to arrange the elements in a
different way. He discovered the modern periodic table of
elements.
■ He arranged them by atomic mass a discovered a repetitive
pattern of several properties (density, metal character, and ability
to react with other elements).
■ Why was he so successful?
– He left blank spaces in the table when necessary to keep
the periodic pattern.
■
He predicted that elements would be discovered to fill them.
–
He was correct. Eventually other atoms were discovered
that filled in the blanks.
More About Mendeleyev
■ https://www.youtube.com/watch?v=fPnwBITSmgU
■ https://www.youtube.com/watch?v=-wu0LixSBpk
Reading the Periodic Table
■ The elements in the periodic table are arranged in
order of increasing atomic number.
■ Atomic Number- atoms in each element has a
unique number of protons. Thus number is used to
classify the atom.
■ Families- the vertical columns contain elements
that react with other substances in similar ways.
■ Period- each row of elements.
■ According to their properties, elements can be
placed in one of three groups.
– Metals- conduct heat and electricity, are
shiny when polished, and bend instead of
break.
– Metalloids- have only some properties of
metals.
– Nonmetals- the opposite of metals.
What Are Metals, Nonmetals, and
Metalloids?
■ About ¾ of the elements are metals.
– Metals conduct electricity.
■
Example- Copper is used in electrical wiring.
■ Nonmetals tend to have the properties opposite of
metals.
– They are poor conductors of electricity.
– They are normally solids of gases at room
temperature.
– Solid nonmetals are brittle instead of bendable.
■ Metalloids properties fall between metals and
nonmetals.
– Used to make computer chips and circuits.
Silicon is a metalloid and is used in
computer chip and found in sand.