# Unit 5: Atomic Structure & The Periodic Table

## 44 terms

### subatomic particles

the particles that make up an atom: protons, neutrons, and electrons

### orbital

a region in an atom where there is a high probability of finding electrons

### wave-mechanical model OR electron-cloud model

modern model of the atom
atoms have electrons in orbitals that are like clouds around the nucleus

### ground-state electron configuration

the most stable (lowest-energy) arrangement of electrons around the nucleus of an atom
listed on the Periodic Table

### excited-state electron configuration

a higher energy arrangement of electrons in an atom that occurs when energy is absorbed and an electron "jumps" to a higher energy level

### bright-line spectrum

also called "emission spectrum"
the lines of colored light given off by atoms as electrons fall to lower energy levels (excited- to ground-state)

### mass number

the mass of an atom
= protons + neutrons

### atomic number

the number of protons in an atom
determines the identity of an atom
Table S
The Periodic Table

### isotopes

atoms of the same element that have different numbers of neutrons (and therefore different masses)

### percent abundance

the percentage of atoms of a particular isotope

### atomic mass

the WEIGHTED AVERAGE of the masses of ALL the isotopes of an element
to calculate:
decimal x mass = products (add)

### valence electron(s)

electron(s) found in the outermost energy level of an atom and that determines the atom's chemical properties

### ion

an atom that is electrically charged (positive or negative)
charge of ion = # protons - # electrons
Ex: a Na+ ion has a charge of +1 (11 protons, 10 electrons)

### atom

smallest unit of matter that retains the properties of an element
electrically neutral (number of protons = number of electrons)

### element

a pure substance made of only one kind of atom
cannot be broken down
Table S
Periodic Table

### nucleus

the positively charged dense center of an atom

### nuclear charge

the number of protons (positive charges) in the nucleus
ALWAYS A (+) NUMBER

### proton

positively charged particle found in the nucleus of an atom
mass = 1 amu
charge = +1

### electron

negatively charged particle found in orbitals outside the nucleus of an atom
mass = almost 0
charge = -1

### neutron

neutral particle found in the nucleus of an atom
mass = 1 amu
charge = 0

### isotope symbol

shows the chemical symbol, mass number, and atomic number for an isotope of an element

### cation

a positively charged ion
has more protons than electrons

### anion

a negatively charged ion
has more electrons than protons

### atomic mass unit (amu)

1/12th the mass of a carbon-12 atom
(unit used to describe the mass of a single atom)

### principal energy level

a region around the nucleus holding a certain number of electrons

distance between the nucleus and outermost electron of an atom

### octet rule

atoms gain or lose electrons to obtain 8 in outer p.e.l. (this is the most stable number of valence e-'s to have)

### reactivity

how an atom gains or loses electrons, when in the presence of other atoms, to become more stable

### ionization energy

the amount of energy required to REMOVE an ELECTRON from an atom
listed on Table S

### electronegativity

a measure of an atom's ATTRACTION for the electrons of another atom
listed on Table S

### period

A horizontal row in the periodic table.

### group

A vertical column on the periodic table
*elements in the same group have similar chemical properties because they have the same number of VALENCE electrons

### electron-dot structure/Lewis-dot structure

a representation of an atom or ion showing the number of VALENCE electrons

### electrical conductivity

the ability to allow electrons to move through a substance

### heat conductivity

the ability to allow heat to move through a substance

### ductile

able to be pulled out into a long wire

### malleable

Able to be bent or shaped

### diatomic element

an element that exists as two atoms bonded together in nature
ex: Br2, I2, N2, Cl2, H2, O2, F2

### metallic character

a measure of how easily an element loses a valence electron (like a metal)

### nuclear reaction

A process that involves a change in the NUCLEUS of an atom

A term that describes a NUCLEUS which is UNSTABLE - one atom turns into a different atom
(radioactive atoms release particles and/or energy from their nucleus to become more stable)

### fission

A type of nuclear reaction in which a massive nucleus splits into smaller nuclei while releasing a lot of energy.

### fusion

A type of nuclear reaction in which small nuclei are joined together to make a larger nucleus while releasing a lot of energy.

### chemical reaction

A process in which the ELECTRONS of atoms are transferred or shared, forming new compounds