n Size (energy level, shell) positive integers (1,2,3,…)

ml Orientation (orbital) (-l to +l)

ppt 2 Flashcards by Anna Kaye Cirujano

Most of the mass is in the ______

nucleus

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containing protons and neutrons

Surrounded by an electron cloud containing electrons in a large volume of space

nucleus

protons + neutrons

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Most of the volume is in the _______

electron cloud

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variation of an element that possesses the same atomic number but a different mass number

any element will always have the same number of protons and electrons

They will differ in the number of neutrons held by their respective nuclei.

isotopes

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the exact location of the electron cannot be known; only the electron density can be known

Quantum Mechanical Model

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the probability that the electron will be in a certain region of space (orbital) at a given instant

Electron density

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Electrons do not circle around the nucleus in fixed orbits but rather in _______

Each _____ has a characteristic shape and size (energy)

orbitals

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used to describe orbitals

QUANTUM NUMBERS

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Principal

n
Size (energy level, shell)
positive integers (1,2,3,…)

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Azimuthal/ Angular Momentum

l
Shape (subshell)
0 to (n-1) / s, p, d, f

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Magnetic

ml
Orientation (orbital)
(-l to +l)

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Electron Spin

ms
Direction
+1/2,-1/2

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each box represents ________

one orbital

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each cluster of boxes represents _________

one subshell

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each row represents ________

one shell

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describes the orbitals occupied by the atom’s electrons when they are all in the available orbitals with the lowest energy

Ground-state electron configuration

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states that an electron occupies orbitals in order from lowest energy to highest (increasing order)

Aufbau Principle

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Every orbital in a sublevel is singly occupied before any orbital is doubly occupied.

All of the electrons in singly occupied orbitals have the same spin (to maximize total spin).

Hund’s Rule

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no two electrons can have the same four electronic quantum numbers.

As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins.

This means if one electron is assigned as a spin up (+1/2) electron, the other electron must be spin-down (-1/2) electron.

Pauli’ Exclusion Principle

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states that we cannot know both the position and speed of a particle, such as a photon or electron, with perfect accuracy;

the more we nail down the particle’s position, the less we know about its speed and vice versa

Heisenberg’s Uncertainty Principle

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electrons below the outermost shell

Core electrons

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electrons in the outermost shell

Valence electrons

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an attractive force between two ions or between two atoms

CHEMICAL BOND

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Why do chemical bonds form?

Because the compound that results is more stable and lower in energy than the separate atoms

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How do chemical bonds form?

Octet rule

atom is most stable if its outer shell is either filled or contains eight electrons, and it has no electrons of higher energy

OCTET RULE

An atom will give up, accept, or share electrons in order to achieve a filled outer shell containing eight electrons EXCEPT _______ and ________

hydrogen and helium

Chemistry of main-group elements is governed by their tendency to take on the electron configuration of the nearest

noble gas

attractive forces between opposite charges

Electrostatic attraction

* bond formed as a result of the electrostatic attraction between ions of opposite charge * bond formed from the transfer of electrons * usually formed from the reaction of metals with nonmetals

Ionic bond

compounds formed by ionic bonds

Ionic compound

bond formed as a result of sharing electrons between two nuclei

COVALENT BOND

compounds formed by covalent bonds

Molecular compounds

measure of the ability of an atom to pull the bonding electrons toward itself

ELECTRONEGATIVITY

a covalent bond between atoms with the same electronegativity

nonpolar covalent bond

covalent bond between atoms with different electronegativities

polar covalent bond

bond where no electrons are shared; opposite charges attract each other

ionic bond

bond where electrons are shared equally

nonpolar covalent bond

Polar molecules have _______

dipoles

a pair of equal and oppositely charged poles separated by a distance

Dipole

- measure of dipole - magnitude of the charge on either atom x distance between the two charges

Dipole Moment

electron-dot structures

Lewis Structures

line-bond structures

Kekulé Structures

DRAWING CHEMICAL STRUCTURES

* Chemical symbols * Covalent bond * Nonbonding/lone-pair electrons * Formal charges

* not an actual charge * used for bookkeeping of electrons * the charge the atom would have if each bonding electron pair in the molecule were shared equally between atoms * the difference between the number of valence electrons an atom has when it is not bonded to any other atoms and the number it “owns” when it is bonded

Formal Charge

formal charge equation

formal charge = no of valence electrons in free atom - no of valence electrons in bonded atoms

omitting of the covalent bonds and listing atoms bonded to a particular carbon (or nitrogen or oxygen) next to it (with a subscript if there is more than one of a particular atom)

Condensed Structures

* Carbon atoms aren’t usually shown. * A carbon atom is assumed to be at each intersection of two lines (bonds) and at the end of each line. * Hydrogen atoms bonded to carbon aren’t shown. * Atoms other than carbon and hydrogen are shown

Skeletal Structures

3D Structures

Perspective Drawing Ball-and-Stick Model Space-Filling Model

shows 3D shape

Perspective Drawing

shows bond angles accurately

Ball-and-Stick Model

shows atoms in scale

Space-Filling Model

bond lies in the plane of the paper

normal bond

bond extends backwards, away from the viewer; "into" the paper bond behind a page

dashed bond

bond protrudes forwards, towards the viewer; bond out of page; "out of" the paper

wedged bond

* Geometry based on arrangement of atoms in a molecule * Defined by bond angles

MOLECULAR GEOMETRY

* Geometry based on valence electron pairs (bonding and non bonding) around a central atom * Bonding electron pairs * Nonbonding/lone electron pairs * Defined by bond angles

ELECTRON PAIR GEOMETRY

A model for the prediction of molecular geometry based on the minimization of electron repulsion between regions of electron density around an atom

VALENCE-SHELL ELECTRON-PAIR REPULSION (VSEPR) MODEL

The best arrangement of a given number of electron pairs (bonding and nonbonding) is the one that

minimizes the repulsions among them.

Without lone pairs: electron pair geometry __ molecular geometry

= equal

assumes that the electrons in a molecule occupy overlapping atomic orbitals of the individual atoms

Valence Bond theory

assumes the formation of molecular orbitals from the atomic orbitals

Molecular Orbital Theory

formed when atomic orbitals on neighboring atoms overlap one another

Covalent bonds

head-on overlap of atomic orbitals; stronger

sideway overlap of atomic orbitals; weaker

atomic orbitals obtained when two or more nonequivalent orbitals of the same atom combine for covalent bond formation

Hybrid orbitals

Produces the molecular geometry of the molecule.

HYBRIDIZATION

one 2s and three 2p orbitals into four sp3 orbitals four sp3 orbitals are 109.5° away from each other → tetrahedral geometry

sp3 Hybrid Orbitals: CH4 (Methane)

one 2s and two 2p orbitals into three sp2 orbitals + one unhybridized p orbital three sp2 orbitals are 120° away from each other: trigonal planar geometry + unhybridized p orbital perpendicular to it

sp2 Hybrid Orbitals: C2H4 (Ethylene)

one 2s and one 2p orbitals into two sp orbitals + two unhybridized p orbital two sp orbitals are 180° from each other → linear geometry + two unhybridized p orbitals mutually perpendicular to it

sp Hybrid Orbitals: C2H2 (Acetylene)

bond strength _____ as bond length ______

increases, decreases

As s character increases, bond angle ________

increases

three sp3 orbitals w/ bonding pairs + one sp3 orbital w/ lone pair (trigonal pyramidal)

two sp3 orbitals w/ bonding pairs + two sp3 orbitals w/ lone pairs (bent)

Single bonds (no π bonds): sp3 w/ lone pairs in the hybrid orbitals

N & O

one sp3 orbital with bonding pair + three sp3 orbitals w/ lone pairs

describes a region of space in a molecule where electrons are most likely to be found

molecular orbital

2 ways to combine atomic orbitals into molecular orbitals

additive and subtractive

lower energy, bonding molecular orbital

Additive

higher energy, antibonding molecular orbital

Subtractive

Occurs when an electron is shared by more than 2 atoms with π bonds (p orbitals)

π ELECTRON DELOCALIZATION

Structures are represented by resonance contributors

π ELECTRON DELOCALIZATION

Some substances can’t be represented by a single line-bond structure and must be considered as a _______ of two or more structures.

resonance hybrid

The two individual line-bond structures are called ________, and their special resonance relationship is indicated by the double headed arrow between them.

resonance forms

It has a single unchanging structure that is a resonance hybrid of the two individual forms and has characteristics of both.

resonance

Individual resonance forms are ______

imaginary, not real

Resonance forms obey normal rules of _______

valency

The _________ is more stable than any individual resonance form

resonance hybrid

resonance leads to

stability

The larger the number of resonance forms, the ____ stable a substance is

vacant p orbital, single electron, or lone pair of electrons on atom Z (resonance forms)

asterisk *

from electron-rich species (negative charge, lone pair, double bond)

tail

to electron-deficient species (positive charge, electronegative atom)

head

between resonance forms

double headed arrow

movement of electrons movement of two electrons movement of one electron

curly arrow curly arrow (full) curly arrow (half)

Double bonds separated by single bonds Refers to a system that has a p orbital adjacent to a π bond allowing delocalization of π electrons

conjugation

Compounds with conjugated double bonds are thermodynamically ____ stable (lower energy) than compounds with isolated double bonds (higher energy).

Special kind of conjugation Cyclic unsaturated molecules with unusual stability Originally used to classify benzene and its derivatives because many of them have distinctive odors

AROMATICITY

Six p orbitals align and overlap to form six molecular orbitals

benzene

TWO CRITERIA FOR AROMATICITY 1. It must have an uninterrupted cyclic cloud of p electrons (called a ____) above and below the plane of the molecule.

p cloud

huckel's rule for aromaticity

Hückel’s Rule: 4n + 2

Not all _______ (carbon ring systems with alternating single and double bonds) are aromatic.

annulenes