part 2 Unit 4 Chemistry test

what is a chemical formula

a set of chemical symbols describing the elements present in a substance and their relative proportions.

what is a chemical symbol

describes the elements present in a substance

what are subscripts

they describe the proportions of elements in the substance

what are coefficients

describe the total number of particles

why do ionic compounds have high melting points

because there is a strong attraction between ions in the crystal , and it requires lots of energy to separate into a liquid

why are ionic compounds brittle

if ions are forced together, they repel and shatter the crystal

why are ionic compounds soluble/dissolve in water

water molecules attract ions and mix with them

why don’t ionic compounds conduct electricity as solids

electrons in ionic compounds are locked into ions. so none can flow through crystal. however they can conduct in water because electrons can flow freely

how do you determine the charge of a transition metal? why do roman numerals need to be included in the compound names for transition metals

You determine a transition metal's charge by balancing the known charges of the anion in the compound, and Roman numerals are essential because most transition metals form ions with multiple possible charges

define close packed structure

atoms in metals are closely packed in crystal structure

what is a electron sea

positive metal ions in a sea of electrons

what is “Delocalized”

valence electrons that are free to flow and move

what is ductile

the ability of a metal to be drawn out into a wire

describe the structure of metals

positively charged metal ions surrounded by a sea of delocalized electrons

why are metallic bonds good conductors

valence electrons are free to flow and move which allows the electricity to flow through the crystal.

why are metallic bonds malleable

because positive nuclei can slide and move over each other within the electron sea

why are metallic bonds lustrous

free valence electrons absorb energy easier and jump to higher energy levels as they drop they release photons.

why are molecular covalent substances poor conductors

because valent electrons are locked into covalent bonds aka not free to flow

why are molecular covalent substances soft

they have a weak attractive force between molecules

why do molecular covalent substances have low boiling points

the same reason why they are soft-they have a weak attractive force between molecules-it takes less energy

why are network covalent solids hard

valence electrons connect atoms in all directions in a grid network

why are network covalent solids poor conductors

valence electrons are locked in place

why are network covalent solids poor conductors

strong covalent bonds hold atoms within the grid structure and it takes a lot of energy to move them