Unit 4 chapter 7&8 - bonding

what are the exceptions to the octet rule (H, He, B)?

-H and He: only need 2 electrons in outer energy level -Be: only needs 4 electrons in outer energy level -B: only needs 6 electrons in outer most level -expanded octets: can have more than 8 in their outer energy level...anything beyond 2nd energy level.

why dont elements always share electrons equally in a covalent bond?

When atoms share electrons unequally, the side that has the greater attraction for the electron has a slight negative charge.

intermolecular forces

forces of attraction between molecules

covalent bonds

involves the sharing of electron pairs between atoms.

what is the octet rule?

is a general rule of thumb that applies to most atoms. Basically, it states that every atom wants to have eight valence electrons in its outermost electron shell.

VSEPR shape names (all 5)

linear trigonal planar tetrahedral trigonal pyramidal bent

diatomic molecules

molecules made up of two atoms of the same element

chemical bonds

physical phenomenon of chemical substances being held together by attraction of atoms to each other through sharing, as well as exchanging, of electrons -or electrostatic forces.

lone pair electrons

refers to a pair of valence electrons that are not shared with another atom and is sometimes called a non-bonding pair

conductivity

the degree to which a specified material conducts electricity, calculated as the ratio of the current density in the material to the electric field that causes the flow of current. It is the reciprocal of the resistivity.

why does an element gain or lose electrons in an ionic bond?

the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion

polarity

the property of having poles or being polar.

melting point

the temperature at which a given solid will melt.

How are polar covalent bonds formed?

when the shared electrons between atoms are not equally shared. This occurs when one atom has a higher electronegativity than the atom it is sharing with.

non polar covalent bonds

with equal sharing of the bond electrons, arise when the electronegativities of the two atoms are equal.

how to identify VSEPR shapes

1. Write the Lewis dot structure of the molecule. That gives you the steric number (SN) — the number of bond pairs and lone pairs around the central atom. 2. Use the SN and VSEPR theory to determine the electron pair geometry of the molecule. 3. Use the VSEPR shape to determine the angles between the bonding pairs.

bent shape

104.5 degrees

trigonal pyramidal

107.3 degrees

tetrahedral shape

109.5 degrees

trigonal planar

120 degrees

linear shape

180 degrees

ionic bonds

A chemical bond formed between two ions with opposite charges. Ionic bonds form when one atom gives up one or more electrons to another atom.

anion

A negatively charged ion

why do elements share electrons in a covalent bond?

By sharing their outer most valence electrons, atoms can fill up their outer electron shell and gain stability / make it stable.

how are cations and anions formed?

Cations (positive) and anions (negative) are formed when a metal loses electrons, and a nonmetal gains those electrons.

organic compound

Compounds that contain carbon

predict the type of bonding between two elements based on their electronegativity differences or their location on the periodic table

Electronegativity is the relative ability of an atom to attract electrons in a chemical bond. 65. ... If the difference is less than 0.4, the bond is considered nonpolar covalent; between 0.4 and 1.7 is polar covalent, and above 1.7 is ionic.

how do intermolecular forces differ from intramolecular forces?

Intramolecular forces are the forces that hold atoms together within a molecule. Intermolecular forces are forces that exist between molecules.

what is the relationship between lone pairs of electrons on polarity?

Larger molecules, even if they have only one kind of atom, are sometimes polar. This will occur when the central atom has one or more pairs of nonbonded electrons.

how are ionic bonds formed?

The bond is formed when an atom, typically a metal, loses an electron or electrons, and becomes a positive ion, or cation.

polar covalent

The greater the electronegativity difference, the more ionic the bond is. Bonds that are partly ionic

malleability

The reason metals bend or dent when struck is linked

How are non polar covalent bonds formed?

These shared electrons glue two or more atoms together to form a molecule.

describe the relationship between lone pairs of electrons and polarity

This will occur when the central atom has one or more pairs of nonbonded electrons. -lone pairs have 2 electrons side by side on LDD. -non lone pairs have a line connecting 2 electrons

What is a single bond?

a chemical bond in which one pair of electrons is shared between two atoms.

what is a triple bond?

a chemical bond in which three pairs of electrons are shared between two atoms.

what is a double bond?

a chemical bond in which two pairs of electrons are shared between two atoms.

Electronegativity

a measure of the tendency of an atom to attract a bonding pair of electrons

cation

a positively charged ion

electrostatic forces

attraction or repulsion of particles or objects because of their electric charge.

use the VSEPR model to describe shapes of molecules

electron pairs in the valence shell of an atom repel each other; their molecular geometry is the result of this repulsion