Chemical Bonding Unit Test

This set might have more than necessary bc I was trying to make it fast, currently unreviewed/edited in terms of amnt of content (refer to the posted study guide for topics) *what he said in jan.* Metallic bonding = 5% test Covalent bonding= 75% test Ionic bonding= 20% test

Central atom

Atom in the center of the lewis structure, forms most bonds, is the least EN (NEVER H)

How to know a central atom in a lewis structure

USUALLY the first element listed in the chemical formula OR look for least EN

exceptions:

- diatomic compounds (2 atoms)

-Hydrogen is the starting element

Single dots (lone e-) on a Lewis structure show…

Bonding sites & if you count them up the ideal # of bonds

Can you reduce the formula of a covalent compound

NO, NEVER.

Formal charge equation

FC= VE-CB-NE

The # of valence electrons (from periodic table) - # of covalent bonds on the atom (on the LS) - # of non-bonded e- (on the LS)

-Do this for each atom in the compound and then add up their charges to see the compounds overall charge

-Most stable is zero UNLESS it’s a polyatomic in which case it would be the charge of the polyatomic that is most stable

Polyatomic ions

Polyatomic’s have both ionic and covalent character (covalently bonded cluster of atoms with an ionic charge)

How to show polyatomic ions lewis structure

Put the compound in parentheses and put the charge on it’s upper right corner

Things that have multiple bonds are more ___ than single bonds

Conductive

this is bc the transfer of e- is quicker & more efficient

Resonance structures

Resonance structures show the multiple ways bonding can occur in a compound

Why are resonance structures caused

They are caused when there is more than one way to place double bonds and lone pairs on atoms

Coordinate bond

When both bonding e- are donated by a single atom

ie. this happens when one atom is satisfied and another isn’t, the satisfied atom will share 2 of it’s e with the other atom, forming a bond, to satisfy it so the whole compound can be more stable

Multiple bonding

Double or Triple bonds

-these occur to satisfy atoms that do not fulfill the octet rule

Why are excess atoms theorized to happen

The D sub-level acts like a trunk where extra e- can be stored if need be, this is why we can fit 10 e- on some atoms instead of only eight, bc 2 would be in the “trunk”

The bonds are SPD hybrids when this happens

How many e- can Sulfur hold?

12*

*only when acting as a central atom!

How many e- can Phosphorus hold?

10*

*only when acting as a central atom!

How many e- can Hydrogen hold?

2

How many e- can Boron hold?

6*

*only when acting as a central atom!

How many e- can Beryllium hold?

4*

*only when acting as a central atom!

*Note, this is a metal but it’s EN is close to NM so it can covalently bond

What are the deficit atoms

Atoms that are stable with less than 8 e-

These are H, B, Be

What are the excess atoms

Atoms that can hold 8+ e- but can be stable @ 8

These are P, S, Noble gases & Halogens (NG and Halogens are VERY rare)

Why are covalent bonds NOT conductive

Bc they do not have charged particles capable of transporting e-

Melting and boiling point increases with…

Molar mass

more mass= more substance to melt

State of matter @ room temp for covalent bonds

Can be solid, liquid, or gas

Why do covalent bonds have low MP/BP

Bc they have weak forces of attraction btwn them. Since covalent bonds form btwn NM’s there is no opposite charges & therefore no coulombic attraction, this makes the force weaker. The e- are also shared, not transferred, making a weaker bond which is easier to break and therefore a lower MP/BP

Properties of covalent bonds

-low melting/boiling point

-soluble (dissociates in water)

-non-conductive

-share e- to achieve octet

How does e- sharing work

Covalent bonds share e- via. orbital overlap

-more overlap (ie. double & triple bonding) = stonger bond

Covalent bonds occur so that…

They can act like noble gases (and be stable)

What is the rep. particle name for covalently bonded atoms

Molecule

Covalent bonds are formed btwn…

Non-metals only*

They share electrons

*Some metalloids bond with nonmetals and tend to form covalent bonds

Lone pair/unshared pair

pair of e- that are NOT shared btwn atoms

Where does hybridization occur

ONLY on the central atom

e- in metallic bonds are located in…

in an e- sea (have to explain on the test what it means), the e- are free-flowing throughout (delocalized) the space btwn each atom

• the size of the e- cloud is dependent on the number of VE contributed

How are the nuclei/cations ordered in a metallic bond

They are in a “crystal lattice” (this is super ordered)

Metallic substances properties

• malleable and ductile

the delocalized e- are a constant presence and are why metallic substances are malleable… the delocalized e- hold together any shifting cations through the electrostatic attraction that exists btwn the e- and the cations

• high melting points

more delocalized e- = tougher metal and higher melting point

• conductive

bc the flow of e- in the electron cloud

ionic bonding have high melting and boiling points bc…

-charge diff. btwn bonded atoms

- stronger charge diff = stronger attraction (= higher mp)

structure of ionic compounds

crystalline solid @ room temp (this is a highly ordered pattern in 3d space)

“Criss Cross” rule

(chemical formula formation)

the charge becomes the subscript for the other element (if you don’t get it idk what to tell you)

ex. K₂O is potassium oxide

Reverse “Criss Cross” rule*

(how to determine charge of d-block/non-rep. elements)

ex. What is the charge of lead in TcO₂

The compound must have a net zero charge, we know how many of each element, and oxygen has a charge of 2- so we can write this into algebra

1x + 2(-2) = 0

1x-4=0

x=4

The charge of technetium would be 4+

How do you tell which ionic compound has a higher melting point

The charge diff. between the bonded atoms in each compound. The stronger the charge diff. the stronger the attraction.

ex. N₂H₄ or H₂O

N₂H₄ has a charge diff. of 4 and H₂O has a charge difference of 3 so N₂H₄ would have a higher melting point

How do you tell which ionic compound is more conductive from the chemical formula

the number of ions in the compound, the more ions the better

ex. N₂H₄ or H₂O

N₂H₄ would have 6 ions and H₂O would have 3 so N₂H₄ would be more conductive

Name into chemical formula

Just do the criss cross with the names given

ex. Magnesium fluoride —> MgF₂

how: Mg²⁺ + F^1- —> MgF₂

Name break down

(metal’s name) (non-metal)oid

ex. Magnesium fluoride

Name break down with roman numerals

“metal’s name” (charge) “non-metal”oid

Roman numeral in parentheses follows the name of the metal to specify its charge

ex. FeCl₂ is iron(II) chloride

ex. Cu₂S is copper(I) sulfide

How to know molecular geometry

The number of domains on the central atom and amount of lone pairs on the central atom

How to tell if a molecule is polar

• bonded e- are shared unequally

How to tell if a molecule is nonpolar

• ANY diatomic molecule (bc the atoms have the same EN and so they pull the e- the same amnt)

• Perfectly symmetric molecules

  • If two atoms are on opposite sides of a central atom and are pulling w/ the same EN then the pulls cancel out and the molecule is NP

• !! Carbon and Hydrogen bonded is considered NP bc they have EN that are super close !!

How to tell if a molecule has polar bonds vs is polar

• Most every molecule has polar bonds except for diatomics (this is bc diatomics have the same EN)

• Molecules can have polar bonds but be nonpolar

  • ex. if two atoms are on opposite sides of a central atom, they would have polar bonds w/ the central atom, but since they and are pulling w/ the same EN then the pulls cancel out and the molecule is NP

How to show bond dipoles

Two options

a. with arrows

• the arrow points toward the more EN atom and the dash in the line goes on the less EN side

b. with the delta symbol (δ+ and δ-)

• The more EN atom would get the δ- (bc it would get more e-) and the less EN atom would get the δ+ (bc it loses the e-)

Why things dissolve

• Like dissolves like bc…

  • nonpolar solutes don’t have dipoles so the dipoles in the polar solvent won’t pull apart the molecules but with polar solutes and polar solvents the positive and negative dipoles are attracted to each other and pull molecules apart

London Dispersion Forces (LDF)

• weakest of all IMF

• !! ALL SUBSTANCES/MOLECULES EXPERIENCE LDF !!

• the more e- a molecule has, the stronger the LDF’s are

Dipole-Dipole Forces

• occur when the partially + charged part of a molecule interacts w/ the partially - charged part of another molecule

• strong relative strength

Hydrogen Bonding

• special kind of dipole-dipole bonding

• Occurs btwn a Hydrogen atom and a Oxygen, Nitrogen, or Fluorine atom

  • The partially positive end of the H in one atom is attracted to the partially negative end of the O,N, or F of another atom

• STRONGEST of dipole-dipole attractions

How to tell a central atom’s hybridization

You count the amount of domains a central atom has and then you fill in the boxes to see how many levels it has (makes more sense with the example)

Bond order & length

The length of the bond is determined by the number of bonded electrons (the bond order). The higher the bond order (more e- in a bond ie. double or triple), the stronger the pull between the two atoms and the shorter the bond length.

Relationship between bond length and strength of bond

If the bond length decreases, the bond energy would increase. If the two atoms bonded are closer together, then by coulomb's law, there should be a stronger force due to a smaller distance. Therefore, a shorter bond length would make it harder to break the bond, resulting in a higher bond energy.

The diatomics

Hydrogen, Nitrogen, Fluorine, Oxygen, Iodine, Chlorine, and Bromine