Transcript Chemistry

• Matter is anything that has volume and mass.
• All matter is made of substances called
elements.
• An element is a substance that cannot be
broken down into simpler substances by
physical or chemical means.
• Elements are made up of atoms.
•
All atoms consist of even smaller particles—protons,
neutrons, and electrons.
• The center of an atom is called the nucleus, which is
made up of protons and neutrons.
•
A proton is a tiny particle that has mass and a
positive electric charge.
• A neutron is a tiny particle with approximately the
same mass as a proton, but it has no electrical
charge
• Surrounding the nucleus of an atom are electrons,
smaller particles that are in constant motion.
• An electron has little mass, but it has a negative
electric charge that is exactly the same magnitude as
the positive charge of a proton.
In this
representation of
an atom, the
fuzzy area
surrounding the
nucleus is
referred to as an
electron cloud.
The periodic table of the elements is arranged so
that a great deal of information about all of the
known elements is provided in a small space.
•
Generally, each element is identified by a
one-, two-, or three-letter abbreviation known
as a chemical symbol.
•
All elements are classified and arranged
according to their chemical properties in the
periodic table of the elements.
• The number of protons in an atom’s nucleus
is its atomic number.
• The sum of the protons and the neutrons in
an atom’s nucleus is its mass number.
• This diagram of the element chlorine explains
how atomic numbers and atomic mass are
listed in the periodic table of the elements.
•
All atoms of an element have the same
number of protons. However, the number of
neutrons of an element’s atoms can vary.
•
Atoms of the same element that have
different mass numbers are called isotopes.
• The atomic mass of an element is the
average of the mass numbers of the isotopes
of an element.
• Radioactive decay is the spontaneous
process through which unstable nuclei
emit radiation.
• In the process of radioactive decay, a
nucleus can lose protons and neutrons,
change a proton to a neutron, or
change a neutron to a proton.
• Because the number of protons in a
nucleus identifies an element, decay
can change the identity of an element.
The two most abundant elements in the
universe are hydrogen and helium. However,
the two most abundant elements in Earth’s
crust are oxygen and silicon.
 A compound is a substance that is composed of
atoms of two or more different elements that are
chemically combined.
 Compounds have different properties from the
elements of which they are composed.
 Compounds are represented by chemical formulas
that include the symbol for each element followed
by a subscript number showing the number of
atoms of that element in the compound. (ex.
MgCl2)
 A mixture is a combination of two or more
components that retain their identities.
 When a mixture’s components are easily
recognizable, it is called a heterogeneous mixture.
 In a homogeneous mixture, also called a solution,
the component particles cannot be distinguished,
even though they still retain their original
properties. A solution can be liquid, gaseous, or
solid
Solids are substances with densely packed
particles, which can be ions, atoms, or molecules.
Most solids are crystalline structures because the
particles of a solid are arranged in regular geometric
patterns, giving solids definite shape and volume.
An increase in temperature increases the
thermal vibrations of atoms in a solid.
When thermal vibrations become vigorous
enough to break the forces holding the solid
together, the particles can slide past each
other, and the substance becomes liquid.
Liquids take the shape of the container they
are placed in, but they do have a definite
volume.
• Some vibrating particles can gain
sufficient thermal energy to escape a
liquid.
• This process of change from a liquid to
a gas at temperatures below the boiling
point is called evaporation.
• Gases, like liquids, have no definite
shape. Gases also have no definite
volume unless they are restrained by a
container or a force such as gravity.
Deposition
Evaporation
 A chemical change rearranges the actual bonds
between the atoms of a substance, creating one or
more entirely new substances.
 Some of the properties that can change with a
chemical change include
 Smell
 Taste
 Color
 Melting and boiling points
 Evidence that a chemical change has occurred includes
 Bubbling
 Changes of color,
 taste,
 smell
 Change of temperature
 During a physical change, chemical properties of a
substance are not changed.
 Some of the properties that can change during a
physical change include
 Size
 Shape
 State of matter
 Some examples of ways to affect physical changes are
 Melting,
 freezing,
 cutting,
 combining,
 dissolving
 Diluting
 Food coloring in water
 Physical (diluting)
 Frying a pancake
 Chemical (you can’t separate the ingredients back out,
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they have chemically rearranged)
Melting ice
Physical (phase change)
Plant growth
Chemical (take water and carbon dioxide and turn it
into more plant!)
Chopping an onion
physical
 More practice in a lab tomorrow!
 Don’t forget a hair tie if you have long hair