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UCR / Chemistry / CHEM 1 / What is the relationship between the number of dots around the chemica

What is the relationship between the number of dots around the chemica

What is the relationship between the number of dots around the chemica


School: University of California Riverside
Department: Chemistry
Course: Preparation for General Chemistry
Professor: Hill harman
Term: Fall 2018
Cost: 50
Name: General Chemistry Midterm #2 Study Guide
Description: This study guide covers Chapters 4, 5 and 6.
Uploaded: 10/19/2018
6 Pages 77 Views 2 Unlocks

AWong (Rating: )

Midterm Review 

What is the relationship between the number of dots around the chemical symbols and the number of valence electrons?

Types of Chemical Bonds


- Do not exist as discrete molecules

- Almost always a solid at room temperatures

- Dissolve readily in water (very good a stabilizing charges)

- Most are made up of a metal and a nonmetal


- Electron sharing occurs

- Electrons feel others atom nucleus

- Delocalization (electrons are not shared in a specific location) Don't forget about the age old question of How do you find the area of a triangle with 2 sides and an angle?


- Form of bonding present in metals (2-3, 6 atoms)

- Conductive

- Do not have well-defined bonds

Electronegativity - relative ability of an atom to attract electrons to itself

How many valence electrons will magnesium lose to have the same electron configuration as a noble gas?

Polar Covalent Bonds 

- Unequal sharing of bonding pair of electrons between atoms

- Results in uneven distribution in charge

Bond Polarity 

- Partial negative and positive charges

- Direction of polarity indicated by arrow pointing to more negative end of bond with + sign at positive end

- Increases as ∆EN increases

Lewis Theory

- Gilbert N. Lewis (1916)

- proposed that atoms form chemical bonds by sharing electrons to acquire configuration of a noble gas

Octet Rule - atoms tend to lose, gain, or share electrons to obtain a set of 8 valence electrons

How many pairs of electrons are shared in a single bond?

We also discuss several other topics like What is meant by quantized energy?

● Lewis Symbols (Dot structures) 

- Chemical symbol for an atom surrounded by one or more dots representing valence electrons

- “Dots” are arranged around elemental symbol

● Lewis Structures: Ionic Bonds 

- A nonmetal and a metal

- Metals lose valence electrons to achieve noble gas electron configuration - Non-metal gain electrons to achieve noble gas electron configuration ● Lewis Structures: Molecular Compounds 

- Pair of electrons are shared between two atoms in a covalent bond

- Single bond signifies the sharing of one pair of electrons

- Lone pair of electrons are those not shared Don't forget about the age old question of How do receptors send information to the brain?

● Drawing Lewis Structures 

1. Determine the number of valence electrons

2. Arrange atoms in a pattern that shows how they are arranges

3. Complete octets of atoms connected to central atom by adding lone pairs 4. Compare the number of electrons in structure to the number determined in step 1 5. If there are remaining electrons, place them around the central atom 6. Complete the octet around central atom (if needed) by converting one or more pairs of lone pairs on adjacent atom into bonding pairs Don't forget about the age old question of How are mature t cells produced and selected in the thymus?

Resonance - when two or more equivalent lewis structures can be drawn for one compound Q: How can I determine which resonance structure is the best?

A: Pick the structure where formal charges are equal to 0 or close to 0. Pick the one with negative formal charges on the most electronegative element.

Formal Charge 

- Determined by the difference between the number of valence electrons in the free atom and the sum of the lone pair in +½ bonding electrons in a molecule

- Artificial way of determining charge

Exceptions to the Octet Rule: 

1. Molecules have odd number of electrons = free radius If you want to learn more check out What is meant by precedent?

2. Molecules with atoms having more than an octet = expanded valence shell Bond Length - average distance between nuclei of two bonded atoms

depends on… If you want to learn more check out What is the social goal of negative reciprocity?

- Identity of the atoms

- Number of bonds between them

Bond Order - the number of bonds between two atoms

- 1 for single bond

- 2 for double bond

- 3 for triple bond

Number of bonding electrons - Number of anitbonding electrons 


.Bond Energy 

- Energy need to break 1 mole of covalent bonds in the gas phase (kj/mol) - Breaking bonds consumes energy (+) forming bonds releases energy (-) Calculating ∆HRxn 

Naming Molecular Compounds 

- Compounds contain of nonmetals

- The first words are the name of the first element in the formula - The second word, change the ending of the second element to -ide - Use prefixes to indicate the number of atoms of each element in the molecules

 → do not use the prefix mono- when naming the first element  → prefixes ending with o- or a- are modified when used with elements  ending with vowels

Naming Ionic Compounds 

- Ionic compounds consist of cations (usually metals) and anions (usually nonmetals) - Cation named first using the name of the element

- Anion named by adding the -ide suffix to name of element

- Formulas must be neutral

Ex: Chlorine → Chloride

Binary Ionic Compound 

- Chemists historically used the latin name of the metal modified with suffixes -ous for lower charge and -ic for higher charge

Stock System 

- Name of the cation is the name of the element with a roman numeral in parentheses to the charge

Ex: Write the name of the following compounds

a) NaCl Sodium Chloride 

b) CrCl3 Chromium(ll) Chloride

Polyatomic Ions - charged group of two or more atoms joined together by covalent bonds → oxoanions 

- Polyatomic anions containing oxygen in combination with one or more other elements - Most have name based on the name of the element that appears first in the formula, with ending changes to -ite or -ate 

- Some elements form more than two oxoanions

- -ate has one more oxygen than -ite

- Prefix hypo- means one less oxygen

- Prefix per- means one more oxygen

Ex: Write the names of the following compounds

a) Cr(ClO4)3 Chromium(lll) perchlorate 

b) NH4NO3 Ammonium Nitrate 

Naming Acids 

● Binary Acids

- Contain hydrogen and a monatomic anion

- Most common binary acids contain halogens

- Acids Names: “hydro” + halogen base name + “ic” + “acid”

Ex: HBr → Hydrobromic Acid

Molecular Shape 

- chemical/physical properties related to molecular shape

Lewis Structures - shows atoms but not spatial orientations

Molecular Models - shows orientations and bond angles, helps us understand physical and chemical properties

Bond Angle 

- Angle in degrees defined by lines joining the center of two atoms to the center of a thirs atom to which they are covalently bonded

- Not always predictable from lewis structures


● Vespr theory

- A model predicting that the arrangement of valence electron pairs around a central atom minimizes repulsion to produce the lowest energy orientation

● Electron pair geometry

- Three dimensional arrangement bonding of valence electron pairs and lone pairs electrons about a central atom

→ to determine electron pair geometry

1. Draw lewis structure

2. Determine the steric number (SN)

SN = (number of atoms bonded to central atom) + (number of lone pairs around central atom)

● Molecular geometry

- Three Dimensional arrangement of atoms in a molecule

- SN=2 (two atoms bonded to the central atom) linear

- SN=3 trigonal planar

- SN=4 tetrahedral

- SN=5 trigonal bipyramidal

- SN=6 Octahedral

● Central Atoms with Lone Pairs

- Bond angles less than predicted

- Electron pair repulsion

Lone pair = greatest repulsion

Bonding Pair= least repulsion

Atomic Orbitals and Bonds

Valence Bond Theory

- Quantum Mechanics based model

- Covalent bonds- overlap of orbitals

Sigma Bonds 

- Covalent bonds having highest valence electron density between the two atoms along bond axis

Pi Bonds 

- Formed by mixing atomic orbitals bot oriented along the bonding axis in a molecule Molecular Orbital (MO) Theory

- Based on the mixing of atomic orbitals or similar shapes and energies to form molecular orbitals

MO Diagram - energy level diagram for showing the relative energies and electron occupancy of the MOs for a molecule

HOMO - Highest occupied molecular orbital

LOMO - lowest occupied molecular orbital


Chiral molecule - one that is not superimposable on its mirror image

Stereoisomer - isomerism created by differences in orientation of the bonds between atoms in molecules

Enantiomer - one pair of optical isomers of a compound; mirror images that cannot be superimposed

Intermolecular Forces 

- In molecules, atoms are held together by strong covalent bonds (intramolecular forces) - Responsible for many of the macroscopic physical properties of substances - Some molecules may have several forces but the strongest one dominates the behavior of molecules

Dispersion Forces (weakest) 

- dispersion = momentary shift in electron density

Temporary Dipole(induced dipole) 

- Segregation of change produced in an atom of molecule by a momentary uneven distribution of electrons

Polarizability (biggest factor is size) 

- Relative ease with which the electron cloud in a molecule, ion or atom can be distorted

Combination of Forces

- More than one intermolecular force may need to be considered when examining solubility

- Solubility decreases as relative energy of H-bonding decreases and dispersion increase - Hydrophobic - “water fearing” ; interaction that repels water

- Hydrophilic - having a tendency to mix with, dissolve in, or be wetted by water

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