All Things Covalent

QUIZ Topics: Lewis Structures, Resonance Structures, Formal Charge and Properties of Covalent Molecules

Central atom

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