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Chemistry
Chapter 13 & 14 – Atoms & Elements
Name ______________________________
7th grade Science
Period _______
1. Atom – All matter is made of small particles called atoms. Atoms are the building blocks of
matter. Anything that takes up space and has mass is matter. As we have learned matter
consists of any solid, liquid, or gas. Forms of energy such as heat, light, and electricity are not
forms of matter and do not consist of atoms. (pg. 326)
2. Elementary Charge – The smallest unit of electric charge that is possible in ordinary matter is
called elementary charge. Positive & negative charges attract one another. Positive vs. positive
charges repulse one another. Negative vs. negative charges also repulse one another. (pg. 324)
3. Protons and Neutrons – The nucleus of an atom is made up of two particles. These include the
positively charged protons, & the neutrons that have no electric charge (they are neutral). This
makes the overall charge of the nucleus positive. The protons and neutrons are the largest parts of
the atom. They contain more than 99 % of the atoms mass. (pg. 326)
4. Electron – The particles of an atom with a negative charge are called electrons. They are found
swarming around like bees outside the atoms nucleus in a region called the electron cloud. The
electron cloud is more than 10,000 times bigger than the nucleus. If an atom was the size of a
football stadium the nucleus would only be the size of a pea. The electron cloud would
represent the rest of the stadium. An atom almost always has the same amount of negatively
charged electrons as it does positively charged protons. This way they cancel each other out
making the atom neutral (no charge). (pg. 326)
5. Elements – Forms of matter that contain only one type of atom are called elements (copper,
gold, carbon, hydrogen, etc.).
6. Atomic Number – The number of protons in the nucleus of an atom is called the atomic
number. The atomic number determines what element the atom represents. Atoms with
different atomic numbers consist of different elements. Atoms of the same element always have
the same number of protons in the nucleus and therefore the same atomic number. The atomic
number usually equals the amount of electrons in the electron cloud too. (pg. 328)
7. Mass number – The number of protons and neutrons in the nucleus of the atom gives you the
mass number. Example: An oxygen atom has 8 protons and 8 neutrons in its nucleus. Thus the
mass number for oxygen is 16. (pg. 329)
8. Isotopes – Not all atoms of the same element have the same number of neutrons. Atoms of the
same element that have different numbers of neutrons, and therefore different mass numbers,
are called isotopes of one another. Having a different number of neutrons will not change the
element of the atom, but it will change the mass of the atom. Example – The element Carbon
has some common isotopes. Carbon-12 has a mass of 12. It has 6 protons & 6 neutrons that add
up to 12. Carbon-13 is an isotope of carbon because it has 6 protons but 7 neutrons for a mass
of 13. (pg. 329)
9. Stable vs. Radioactive – Almost all elements have one or more isotopes that are said to be
stable because their nucleus stays together. Radioactive isotopes have a nucleus that is unstable
and it breaks apart, emitting particles or energy in the process. This is caused by too many
neutrons in the nucleus. Another isotope of Carbon is Carbon-14. It is radioactive because it
has 6 protons but 8 neutrons making it unstable. (pg. 330)
10. Ion – Some atoms are electrically charged because they have either gained or lost an electron.
An atom that has lost an electron becomes a positive ion because one of the positive protons in
the nucleus is not being cancelled. An atom that has gained an electron becomes a negative ion
because it has an extra negative electron that is not being cancelled by any proton. Ions are
attracted to each other when they have opposite charges (table salt is made up of one ion
of sodium, and one ion of chlorine). .
11. Molecule - Atoms can sometimes combine together by sharing electrons in the outermost
portion of their electron clouds. This is called a covalent bond. The combined atoms form what
is called a molecule.
12. Compound - When the atoms of different elements combine to form a substance that has
different properties from the original elements this is called a compound. Example: When two
atoms of hydrogen gas combine with one atom of oxygen gas liquid water is formed (H2O).
Table salt is also an example of a compound. Molecules are the building blocks of compounds.
Compounds cannot be separated back into their individual elements by any physical means. To
separate them requires a chemical change.
13. Mixtures/Solutions - When several different substances are mixed together without losing
their original properties this is called a mixture. Example: If you mix dirt, gravel, and rocks
you have a mixture. Even though the substances are mixed the dirt is still dirt, the gravel is
still gravel, and the rocks are still rocks. It is important to know that mixtures can be separated
back into their individual substances by physical means. Solutions are mixtures that are
always evenly mixed Example: Sugar and tea
14. Electron Energy Levels – Electrons swarm around the nucleus at different energy levels.
Electrons with higher energy are farther from the nucleus, electrons with lower energy are
closer to the nucleus. There are many energy levels. The first four energy levels are as follows:
The 1st energy level closest to the nucleus can have up to, but no more than 2 electrons.
The 2nd energy level can have up to, but no more than 8 electrons.
The 3rd energy level can have up to, but no more than 8 electrons.
The 4th level farthest out can have up to, but no more than 18. (pg. 336)
15. Physical Properties – As we have learned the properties you can observe through direct
observation are called physical properties. These are properties that we see without changing
something into a new substance. This includes things such as color, size, shape, weight, mass,
volume, texture, hardness, strength, elasticity, brittleness, ductility, phase of matter, melting
point, boiling point, & density. Note: Physical changes are reversible. (pg. 344)
16. Chemical Properties – Characteristics of matter that can only be observed when a substance
changes into a different substance during a chemical change (reaction). It will have different
properties (it will turn into something new). Chemical properties determine how an element
will therefore react with another element. Iron turning into rust when it rains is an example.
Note: Chemical change is very hard to reverse. You cannot usually change it back. (344)
17. Periodic Table – A chart that organizes the elements based on their chemical properties and
increasing atomic number is called the periodic table. Rows on the periodic table are called
periods. Column on the table are called groups. (pg. 345)
18. Metals, Nonmetals, & Metalloids – Elements that are typically shiny and good conductors of
heat & electricity are called metals. Elements that are poor conductors of heat & electricity are
called nonmetals. Elements on the border between metals and non metals are called metalloids.
19. Atomic Mass – The average of all the known isotopes of an element gives the atomic mass
for the periodic table. Atomic mass is different from mass number because it averages all the
various isotopes of an element, instead of just simply adding the protons and neutrons together
like you do to find the mass number of a single atom. (pg. 347).
20. Periodicity – The repeating pattern of chemical and physical properties of the elements is
called periodicity. (pg. 352)
21. Electrical Conductor – A material that allows electricity to flow through easily is called an
electrical conductor. Metals are good electrical conductors. (pg. 353)
22. Thermal Conductor – A material that allows heat to flow through freely is called a thermal
conductor. Metals are also good thermal conductors. (pg. 353)
23. Insulator – A material that slows down or stops the flow of heat or electricity is called an
insulator. Gases are great insulators. (pg. 353)
24. Alloy/Steel – Steel is an alloy of iron and carbon. An alloy is a solid mixture of two or more
elements. (pg. 354)
25. Solution, Solvent, & Solute - Sometimes in a mixture one substance is dissolved in another
substance. These substances are also evenly mixed or distributed. This kind of mixture is
called a solution. Examples: Salt water and sweetened tea. In a solution like this the water
that the tea, sugar, and salt is dissolved in is called the solvent. The tea, sugar, and salt that are
dissolved in the water are called solutes. (pg. 40)
26. Dissolve - When you break something down into smaller particles using a solvent like water
you are dissolving that substance.
27. Solubility - How easy something will dissolve is called its solubility.