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SAC Biology 1406 Chapter 2


that which has mass and occupies space


(physics and chemistry) the smallest component of an element having the chemical properties of the element


groups of two or more atoms held together by chemical bonds


any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter - Pure substances that cannot be broken down


a stable particle with positive charge equal to the negative charge of an electron


an elementary particle with 0 charge and mass about equal to a proton


an elementary particle with negative charge

atomic nucleus

An atom's central core, containing protons and neutrons.


regions around the nucleus in which given electron or electron pair is likely to be found

Energy Shell

energy levels that contain electrons

Valence Electron

an electron in the outer shell of an atom which can combine with other atoms to form molecules

Atomic Number

the number of protons in the nucleus of an atom

Atomic Mass

(chemistry) the mass (in atomic mass units) of an isotope of an element


a measure of mass for atoms and subatomic particles; the same as the atomic mass unit, or amu.


the molecular weight of a substance expressed in grams

Avogadro's Number

number of representative particles in a mole, 6.02 X 10^23


atoms of the same element that have different numbers of neutrons


isotopes that have unstable nuclei and undergo radioactive decay

Trace Elements

an element indispensable for life but required in extremely minimum amounts

Molecular Formula

2 or more of same atom combined


(chemistry) a substance formed by chemical union of two or more elements or ingredients in definite proportion by weight

Covalent Bonds

a type of strong chemical bond in which two atoms share one pair of valence electrons

Octet Rule

States that atoms lose, gain or share electrons in order to acquire a full set of eight valence electrons

Double Bond

a covalent bond in which two pairs of electrons are shared between two atoms


(chemistry) the tendency of an atom or radical to attract electrons in the formation of an ionic bond

Polar Covalent Bonds

a type of covalent bond between atoms that differ in electronegativity. the shared electrons are pulled closer to the more electronegative atom. making one slightly negative and the other slightly positive

Nonpolar Covalent Bonds

bonds in which electrons are shared equally between two atoms of the same element in a compound.

Polar Molecules

molecules in which the charges are unevenly distributed; they can attract each other

Nonpolar Molecules

Electrically balanced molecules.

Hydrogen Bond

a chemical bond consisting of a hydrogen atom between two electronegative atoms (e.g., oxygen or nitrogen) with one side be a covalent bond and the other being an ionic bond

van de Waals forces

attraction forces between nonpolar molecules that hold them together, which become stronger with higher molar masses


a particle that is electrically charged (positive or negative)


Negatively charged ions

Ionic Bond

a chemical bond in which one atom loses an electron to form a positive ion and the other atom gains to electron to form a negative ion

Element Naming

Element Name
Atomic Number
Atomic Mass

Biology: Chemistry Connection

Based on principles of chemistry & physics all living organisms are collections of atoms & molecules


the vertical force exerted by a mass as a result of gravity


The quantity of matter of an object.

90% of the mass of an organism is composed of 4 elements

Oxygen, Carbon, Hydrogen, Nitrogen





S Orbital

s orbital, have the shape of a sphere, with the center of the sphere at the nucleus; completely symmetrical along all axes; 1s orbital is spherically symmetric and has no nodes; 2s orbital is also spherical but contains a node and is higher in energy

P Orbital

dumbbell shaped orbitals; the second kind of orbital present, can hold a total of 6 electrons in 3 orientations (x, y, z axes)

Periodic Table

Elements organized by Columns left to right indicate # of electrons in the outer shell (Groups) and Rows indicate number of energy shells (Periods)

3 Types of Bonds



positively charged ions

Hydrogen Bonds

very weak bonds; occurs when a hydrogen atom in one molecule is attracted to the electrostatic atom in another molecule

What makes up everything in the universe?


Name 2 properties of all matter

anything that occupies space or has mass

Define mass

the amount of matter in an object

How does weight differ from mass?

Weight is a measure of force, where mass is a measure of the quantity of matter. Can have no weight, but always has mass.

What are elements

Any material that is made up of only one type of atom. Any substance that cannot be broken down into a simpler-one by a chemical reaction. Elements consist of atoms with the same number of protons in their nuclei, and 92 occur naturally on Earth.

Name the 4 elements that make up most of a living thing

nitrogen, oxygen, carbon, hydrogen

What is used to represent an element?

chemical symbol

Name the smallest part of an element


What are the 2 main regions of an atom?

nucleus and electron cloud

Where is the nucleus of an atom found and what does it contain?

the center/the central core; protons and neutrons

What is the charge on a proton?


What is the charge on a neutron?


All atoms of the same element have the ____ number of protons.


The number of protons in an atom determines the ____?

atomic number

What is the charge on an electron?


If you know the number of protons in an atom, how can you determine the number of electrons?


Do all the atoms of the same element have the same number of neutrons?


Atoms of the same element with different numbers of neutrons are called ____


The mass of an atom is centered in the ____


The number of protons plus neutrons in an atom determines its ____

atomic mass

What atomic particle has a negative charge?


Why isn't the mass of an electron used to determine the atomic mass of an element?

Because they have little or no mass.

Where are electrons found?

Electron Clouds

Which electrons in an atom have the most energy?

the ones found furthest from the nucleus (valence electrons)

How many energy levels are there & name them?

7 in total. K, L, M, N, O, P, Q

How many electrons will each energy level hold?

the first hold 2, the 2nd holds 8 and the 3rd holds 8

Elements are arranged on a ____ by their atomic ____

periodic table; number

What are Periods & what do they tell you about elements?

The horizontal rows; tell the number of energy levels

What are Groups & what do they tell you about elements?


Two or more elements combined together make a ____


Chemical ____ represent compounds


____ are the smallest part of a compound


____ in chemical formulas tell the number of atoms of each element


____ in a formula tell the number of molecules


Compounds have ____ properties than its elements


The outermost ____ in elements determine if they will combine


Elements with ____ outer energy levels are stable & won't react


Why do elements tend to react with other elements?

fill the outer shell and become stable

Chemical ____ represent chemical reactions.


____ appear on the right of the equation, while ____ are on the left.

products: reactants

Chemical bonds store ____


How do covalent bonds form?

they are formed when 2 atoms share 1 or more pairs of electrons

How do ions form?

When an atom gains or loses an electron

Positive ions ____ electrons, while negative ions ____ electrons

lose; gain

Define energy

internal motion of particles

Give some examples of different forms of energy

chemical, thermal, electrical, mechanical

Atoms are in constant ____, which determines the atom's ____

motion; state

List the 3 main states of matter

solid, liquid, gas

____ energy must be added or removed to change the state of matter


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