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cem 141 215 (1) Questions & 100% Verified Correct Answers with complete solutions (Latest update
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cem 141 215Atoms are basic particles that compose ordinary matter. Molecules are what atoms become
when they bind together in specific geometrical arrangements. Atom is the smallest particle in
an element. Molecules are formed by the combination of two or more atoms. Unlike atoms,
molecules can be subdivided to individual atoms. The atoms are bonded together in a molecule.
An atom has a nucleus surrounded by electrons. The electrons are negatively charged
particules and the nucleus contains neutrons and positively charged protons. - ANS-What is the
difference between atoms and molecules?
Gases, liquids and solids are all made up of atoms, molecules and ions.
1) Liquid - they are packed close together like solids, but have a weaker attraction allowing them
to move. Liquids have a fixed volume, but not a fixed shape, and take the shape of their
container. Ex: water alcohol, and gasoline are liquids at room temp.
2) Solid - They are packed close to each other in a fixed location due to their strong attraction to
one another. A solid has a fixed volume and a rigid shape.
3) Gas - he attraction between particles is very weak allowing them to move freely and at a
large distance before colliding with one another. Due to the large amount of space between the
particles, gases are compressible. Gases always assume the shape and volume of their
container. Ex: helium, nitrogen, and carbon dioxide at room temp. - ANS-Distinguish between
the 3 states of matter: solid, liquid, gas
Matter can be broken down into two categories: pure substances and mixtures. Pure
substances are further broken down into elements and compounds. Mixtures are physically
combined structures that can be separated into their original components. A chemical
substance is composed of one type of atom or molecule.
1) Mixture - Substance composed of two or more particles in proportions that can vary from one
sample to another
2) Pure Substance - made up of only one type of particle and its composition does not vary from
one sample to the other. Particles that compose a pure substance can be individual atoms or a
group of atoms joined together.
Ex: helium b/c it's made up of helium atoms; water is made up of water molecules; and sodium
chloride is made up of sodium chloride units. - ANS-Differentiate between mixtures and pure
substances
1. Element: substance that cannot be chemically broken down into simpler substances.
2. Compound: substance that is composed of two or more elements.
A compound contains atoms of different elements chemically combined together in a fixed ratio.
An element is a pure chemical substance made of same type of atom. - ANS-Differentiate
between elements and compounds
,1. Heterogeneous Mixture: composition varies from one region of the mixture to another. They
don't mix uniformly.
2. Homogeneous Mixture: have same composition throughout. They mix uniformly. -
ANS-Differentiate between heterogeneous and homogeneous mixtures
Meter (m) = Length
Kilogram (kg) = Mass
Second (s) = Time
Kelvin (K) = Temperature - ANS-I know the SI base units for length, mass, time and temperature
Without units, the results are unclear and it is hard to keep track of what each separate
measurement entails. Units of measurement are the terms that we use to describe the size of
something. You probably know that units include things like seconds, kilograms, meters, and so
forth.
Without standard units of measurement, scientists would have a huge problem understanding
what other scientists were saying. - ANS-Importance of reporting correct units with
measurements
The International System of Units (SI). - ANS-What unit system do scientists use?
Antoine Lavoisier said "in a chemical reaction, matter is neither created nor destroyed". The
total mass of the substances involved in the reaction does not change. - ANS-Law of
Conservation of Mass and who created it
The emission of elementary particles by some atoms when their unstable nuclei disintegrate
(see half-life). Materials composed of such atoms are radioactive. (See alpha radiation, beta
radiation, and gamma radiation.) - ANS-Radioactivity
nucleus is the positively charged center of the atom consisting of protons and neutrons. -
ANS-Nucleus
A positively charged particle within a nucleus ... The number of protons in an element's nucleus
is called the atomic number. - ANS-Proton
Neutral partials witching a nucleus. They contain no electrical charge
subatomic particle found in the nucleus of atoms that differs from the other subatomic particles
(called "protons") in the nucleus of atoms because neutrons have no (zero) charge whereas
each proton has a positive charge of +1. - ANS-Neutron
AMU - 1/12 of the mass of a carbon -12 atom
it is a unit of mass used to express atomic masses and molecular masses. - ANS-Atomic Mass
Unit
The number of protons in a atom's nucleus and is given the symbol Z - ANS-Atomic Number
, an abbreviation of a chemical element, symbols in a periodic table - ANS-Chemical Symbol
An atom that has the same number of protons but different number of neutrons - ANS-Isotope
It is the sum of neutrons and protons in an atom and is represented by the symbol A. It also can
me written as X-A. Ex: Ne-20 - ANS-What is a mass number and the symbol represents it?
abundance of isotopes of a chemical element as naturally found on a planet
when a natural element has a roughly constant percentage of isotopes - ANS-Natural
Abundance
an atom that has obtained a charge - either + or -. - ANS-Ion
- a negatively charged ion - ANS-Anion
- a positively charged ion - ANS-Cation
All elements are defined by a 1 or 2 letter symbol. The atomic number listed on top tells us the
number of protons and vice-versa - ANS-Periodic Table
the measure of how close a measurement is to the actual, exact value - ANS-accuracy
the relative proximity of a set of measurements to each other or how reproducible they are. For
an individual measurement - how many places to the right of the decimal are reported. -
ANS-Precision
Random error is always present in a measurement. It is caused by inherently unpredictable
fluctuations in the readings of a measurement apparatus or in the experimenter's interpretation
of the instrumental reading. - ANS-Random error
. A systematic error (an estimate of which is known as a measurement bias) is associated with
the fact that a measured value contains an offset. This type of error affects all of the data by
shifting it either too high or low. This is an error that is built into the apparatus and can not be
reduced by repeat readings. To remove the size of the error is found and then minused from all
of the results. - ANS-Systematic Error
mass per unit volume of a substance
Relationship between mass and volume D=Mass/Volume - ANS-Density
a property that depends on the type of matter in a sample, not the amount of matter. (Intensive
Properties can be helpful clues to identifying unknown substances.
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