Chapter 2 Biology Study Guide

atom’s central core.

positively charged, found in the atomic nucleus

no electrical charge, found in the atomic nucleus

negatively charged, surround the nucleus in a “cloud” ; orbit the nucleus Can only have 2 electron charges on shell.
– orbit the nucleus of an atom in specific electron shells.
– number of ___ in the outermost shell determines the chemical properties of an atom.

energy levels
represented by electron shells

potential energy
energy that matter possesses because of its location or structure

the capacity to cause change

alternate mass forms of an element. they have the same number of protons and electrons. But they have a different number of neutrons

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atomic number
number of protons of an element

mass number
sum of protons + neutrons in nucleus of an atom.

atomic weight

valence shell
The outermost shell

polar covalent bond
atoms have differing electronegativities; share the electrons unequally.
Example : H2O: O –
+ H + H

nonpolar covalent bond
atoms have a similar electronegativities; share the electron equally.
Example Oxygen gas (O2): O=O

essential elements
include carbon, hydrogen, oxygen, and nitrogen. Make up of 96% of living matter.

ionic bond
an attraction between anions and cations.

Be able to draw example.

hydrogen bond
froms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom.

Be able to draw example.

covalent bond
the sharing of a pair of valence electrons. Forms when two atoms share one or more pairs of outer-shell electrons. Be able to draw example.
Example: H²O: O-H

single bond
sharing of one pair of valence electrons
H²: H-H two hydrogen atoms can form a ____.

double bond
sharing of two pairs of valence electrons
O²: O=O two oxygen atoms share two pair of electrons to form a ___.

atoms with more or fewer electrons than usual; charged atoms.

positively charged ions

negatively charged ions

consists of a certain kind of atom that is different from those of other elements.

consists of two or more atoms held together by covalent bonds.

a substance consisting of two or more elements combined in a fixed ration. Has characteristics different from those of its elements.

valence electrons
those in the outermost, or valence shell. determine the chemical behavior of an atom.

the attraction of a particular kind of atom for the electrons in a covalent bond. the more ____ an atom, the more strongly it pulls shared electrons toward itself.

What is the difference between an element and a compound
Elements and compounds are pure chemical substances found in nature. The difference between an element and a compound is that an element is a substance made of same type of atoms, whereas a compound is made of different elements in definite proportions.

Describe the structure of an atom
smalled unit of matter that still retains the properties of an element. Composed of even smaller parts called subatomic particles.

Define and distinguish among atomic number, mass number, and valence shell
The atomic number is the number of protons, which is located on top of the element symbol. The mass number is the number of protons+ neurons. Located below the element symbol. The valence shell is the outer most shell. It determines the chemical behavior of an atom.

Given the atomic number and atomic weight of an atom, determine the number of neutrons
Number of Neutrons = Mass Number – Atomic Number

How does an isotope differ from a normal atom?

Explain how electron configuration influences the chemical behavior of an atom.

Explain the differences between non polar covalent, polar covalent and ionic bonds.
In a nonpolar covalent bond, the atoms have similar electronegativities. They share the electron equally.
example: O2: O=O In a polar covalent bond the atoms have differing electronegativities; share the electrons unequally.

Describe the formation of a hydrogen bond and explain how it differs from a covalent or ionic bond.

How does an ionic bond differs from a covalent bond?

From the number of electrons in an atom, predict how many bonds an atom might form

How does electronegativity influence the formation of chemical bonds?

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