CHEMISTRY 108 – Help Sheet #1
Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center
http://www.chem.wisc.edu/areas/clc (Resource page)
Nuggets: Atoms, Molecules, Elements, Compounds, Chemical and Physical Properties,
Chemical and Physical Changes, Atomic Structure, Radioactivity
Atom: the smallest particle of an element that has the chemical properties of that element
Molecule: smallest discrete unit of a compound (e.g., H2O(g)) that maintains the chemical characteristics
of that species. Note that some elements exist naturally as molecules (e.g., O2(g)), rather than as free
atoms. (See below for list of important molecular elements.)
Element: a pure substance that contains a single type of atom and can not be decomposed into two or
more substances; one of about 106 unique atoms on the periodic table (e.g., Ag, Fe, or Br2).
Color convention for elements when represented in “Space-filling” and “Ball and Stick” models: Carbonblack, Hydrogen-white, Oxygen-red, Nitrogen-blue
Compound: 2 or more atoms bonded together in fixed proportions (e.g., CO2 or NO); a pure substance
that contains atoms of two or more elements
Chemical Property: how a substance reacts chemically (e.g., C(s) can react with O2(g) to form CO2(g)).
Does it burn (flammable)? Is it inert (unreactive)?
Physical Property: characteristics of chemicals (e.g., boiling/melting point, density, radioactivity, etc.)
Chemical Change: a chemical reaction has occurred and the atoms are rearranged to form new species.
Note that the quantity of each type of atom does not change during a chemical reaction, and atoms of one
element are never changed into atoms of a different element during a chemical reaction.
Physical Change: a change in phase of matter (e.g., H2O(s) to H2O(l))
ATOMIC STRUCTURE
Nucleus: contains protons (+1 charge) and neutrons (0 charge). All the mass of the atom is in the
nucleus, which is tiny and extremely dense.
Electron Cloud: contains electrons (-1 charge). The radius and volume of the atom are determined by
the electron cloud. The electron cloud surrounds the nucleus.
Particle Relative Mass Actual Mass (kg) Relative Charge
Electron
Neutron
Proton
Location
~0
9.11*10-31
-1
Electron Cloud
~1
1.67*10
-27
0
Nucleus
1.67*10
-27
+1
Nucleus
~1
The atomic number is the number of protons in the nucleus of an atom. An element is defined by the
number of protons in its nucleus.
The Periodic Table is arranged in order of increasing atomic number. Each element has a chemical
symbol, consisting of either a single capital letter (e.g. H, N, I) or a capital letter followed by a lower case
letter (e.g. Cl, Na, Br).
Some elements exist in molecular form. For instance, there are seven diatomic elements which you
should memorize for this course:
Hydrogen (H2)
Nitrogen (N2)
Oxygen (O2)
Fluorine (F2)
Chlorine (Cl2) Bromine (Br2)
Iodine (I2)
A mnemonic for memorizing the diatomic elements is: BrINClHOF
Most chemicals in nature exist as compounds, not elements.
It’s often impossible to visually distinguish between an element and a compound.
Your body is primarily composed of just 11 elements. These elements make up 99% of your body (by
mass). Within your body, these elements exist primarily in the form of compounds.
There are some elements which exist in trace amounts on planet Earth. These rare elements are often
extremely expensive.
Radioactivity
Radioactivity: spontaneous emission of ionizing radiation (alpha, beta, or gamma) from an unstable
nucleus
Isotopes: two or more forms of a single element that differ in the number of neutrons in the nucleus.
Different isotopes of an element have different relative abundances in natural samples of an element.
Different isotopes of the same element have identical chemical properties, but they differ in mass.
Radioisotope: an isotope of an element that is radioactive. All elements have some radioisotopes. All
isotopes of elements beyond element 83, bismuth, as well as elements 43, technetium, and 61,
promethium, are radioisotopes.
Alpha decay: radioactive decay involving emission of an alpha particle. Results in a new element plus an
alpha particle. A radioisotope is likely to undergo alpha decay if its “nucleus is too heavy.”
Alpha Particle: a positively charged particle consisting of one Helium-4 nucleus, which is composed of 2
protons & 2 neutrons.
Symbolized as 24 He or 24 α
Beta decay: a nuclear decay in which the radioisotope is transformed into a new element with one more
proton and one less neutron, and a beta particle is emitted. Beta decay is likely to occur if the “nucleus
has too many neutrons.”
Beta Particle: a high energy electron emitted from the nucleus
Symbolized as −10 e or −10β
Gamma ray: extremely high energy electromagnetic radiation. Gamma rays are often emitted during
radioactive decay.
Symbolized as 00 γ
Ion: an atom or molecule with a non-neutral charge caused by loss or gain of electrons
CHEMISTRY 108 – Practice Questions Week 1
Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center
http://www.chem.wisc.edu/areas/clc (Resource page)
1. Name the elements: a) Pu = _____________ b) Pb = _______________ c) Hg = _______________ d) Fe = ________________ e) Na = ______________ f) N = ______________ 2. Give the symbol and atomic number for each element: a) carbon _____ _____ b) chlorine _____ _____ c) radon _____ _____ 3. Identify each statement as a description of a physical property, chemical property, physical change, or chemical change. a) Mercury is a liquid at room temperature.__________________ b) Wood is burned to heat your home. _________________ c) Wet clothes are hung on the clothesline to dry. _______________ d) Ice is less dense than liquid water. ______________ e) Hydrogen gas is flammable. ________________ f) Nitrogen gas is inert. _______________ 4. a) List three renewable resources: ________________ _______________ _______________ b) List three nonrenewable resources: ________________ _______________ _______________ 5. Fill in the table: Particle Charge Relative Mass Location Proton 0 0 6. Fill in the table: Isotope Symbol Atomic number Neutrons Mass Number 208
82 Pb 47 110 Cl 18 7. a) Give three examples of elements that exist as molecules. (Give their names and symbols.) 1) ___________________ 2)_____________________ 3) ____________________ b) Give three examples of molecular compounds. (Give their names and symbols.) 1) ___________________ 2)_____________________ 3) ____________________ c) Give three examples of elements that exist as atoms. (Give their names and symbols.) 1) ___________________ 2)_____________________ 3) ____________________ d) Can you give an example of a compound that exists as atoms? (Explain.) CHEMISTRY 108 – Practice Questions Week 1 - KEY
Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center
http://www.chem.wisc.edu/areas/clc (Resource page)
1. Name the elements: a) Pu = __plutonium__ b) Pb = __lead__ c) Hg = __mercury__ d) Fe = __iron__ e) Na = __sodium__ f) N = __nitrogen__ 2. Give the symbol and atomic number for each element: a) carbon __C__ __6__ b) chlorine __Cl__ __17__ c) radon __Rn__ __86__ 3. Identify each statement as a description of a physical property, chemical property, physical change, or chemical change. a) Mercury is a liquid at room temperature. __physical property__ b) Wood is burned to heat your home. __chemical change__ c) Wet clothes are hung on the clothesline to dry. __physical change__ d) Ice is less dense than liquid water. __physical property__ e) Hydrogen gas is flammable. __chemical property__ f) Nitrogen gas is inert. __chemical property__ 4. a)List three renewable resources: __solar__ __wind__ __water__ __timber__ b) List three nonrenewable resources: __crude oil__ __coal__ __natural gas__ __metal ores__ 5. Fill in the table: Particle Charge Relative Mass Location +
Proton 1 1 In nucleus Neutron 0 1 In nucleus -­‐
Electron 1 0 Outside nucleus 6. Fill in the table: Isotope Symbol Atomic number Neutrons Mass Number 208
Pb (lead) 82 126 208 82 Pb 110
47 Ag 35
17 Cl Ag (silver) 47 63 110 Cl (chlorine) 17 18 35 7. a) Give three examples of elements that exist as molecules. (Give their names and symbols.) 1) hydrogen (H2) 2) oxygen (O2) 3) nitrogen (N2) b) Give three examples of molecular compounds. (Give their names and symbols.) 1) water (H2O) 2) carbon dioxide (CO2) 3) carbon monoxide (CO) c) Give three examples of elements that exist as atoms. (Give their names and symbols.) 1) neon (Ne) 2) helium (He) 3) radon (Rn) d) Can you give an example of a compound that exists as atoms? (Explain.) No. A compound must contain at least one atom of at least two different elements.