Ch. 1 RECAP practice questions

what of daltons theory still hold?

atoms can be broken down into subatomic particles, atoms can have different isotopes and masses, chemical reactions due to rearranging atom so they neither created nor destroyed by chemical reactions

what are london dispersion forces?

attractive forces that exist between particles

what happens to PE and KE when 2 HE atoms begin to approach?

PE decreases cause attractive forces are at play

KE increases cause attractive forces make atoms begin to move in

what happens to KE and PE when 2 HE atoms get TOO close and collide?

PE increases sharply because of the collision between electron clouds

KE decreases because PE increases and atoms in closed system

what happens to the total energy when atoms move positions in a closed system?

total energy stays the same due to the conservation of energy

what happens to Total Energy when a 3rd atom is introduced into the system?

the total energy—>decreases

cause new atoms takes energy away from original 2 atoms and when they collide again they get stuck together, stuck in energy well

what doe sit mean when atoms are stuck in an energy well?

they dont have enough energy to overcome the interaction

what does it mean when atoms don’t sit in the PE well?

they have TOO much energy to remain still

why do atoms move towards each other

because of attractive LDF’s between them

why do atoms oscillate?(move back & forth)

because they don’t have enough energy to move FURTHER apart from each other cause they in closed system

what does a 3rd atoms act as

acts as energy transfer and remove total energy form system, & allows original 2 atoms to stick together

what is the mechanism of energy transfer?

collision between objects

how does a stable interaction form?(how atoms odn’t fly apart)

by removing energy from a system

how energy normally added or removed from 2 atoms?

you either increase or decrease temp

whee would an increased amount of energy in a system go?

the energy will come and go from its surroundings

what happens to atoms energy when temp is increased?

kinetic energy is increased and they move faster

what prevents He atoms from separating/how do they stick together?

london dispersion forces,

how do atoms overcome london dispersion forces?

add energy to system of atoms to overcome LDF’s

when you add thermal energy to He atoms?

kinetic energy increases, atoms move faster, they collide w/ each other, then they get enough energy to overcome LDF(attractive force) between them, they fly apart

whats the relationship between thermal energy and temp?

thermal energy is the average KE of an atom

temperature is directly related to KE average in genreal

how do He atoms know the temp is rising?

they begin to move faster and collide w/ their surroundings because of the increase thermal energy

when atoms @ far distance but begin to move closer, whats the strongest force?

attractive force between atoms

at PE minimum, whats the strongest force?

attraction=repulsion, at bottom of well is most stable interaction

when atoms move in even closer and collide, whats the strongest force?

repulsion between the 2 very very close atoms

what does the depth of the PE well tell us?

how much energy is needed to overcome the interaction, stronger interaction=deeper well

what can the position on the x-axis of PE well tell?

the distance between the 2 nuclei of 2 atoms

what does a solid phase look like for He atoms look like?

particles packed together tightly in uniform arrangement

what does a liquid phase for He atoms look like?

particles not as organized & occupy shape of container

what does a gas phase look like for He atoms?

particles far apart, not interaction at all

He has 2 electrons, Xe has 54 electrons, what can be interpreted about the size of its electron cloud?

Xe has a larger electron cloud than He does

how do we compare sizes of atoms?

by comparing their Van Der Waals radius

what does it mean for electrons to be further away from the nucleus?

it means they feel less of an attractive force

what happens to an electron cloud if the electrons are further away from the nucleus?

the cloud will be more floppy/polarizable

compared to He, the LDF’s for Xe are expected to be lesser or greater?

greater because Xe has more electrons and its cloud is more polarizable

how is the strength of London dispersion forces determined?

they increase w/ the size of particle(the # of electrons)

what does it mean for an atom to have more surface area in terms of intermolecular forces?

the london dispersion forces will be stronger because there more areas to interact

does He or Xe have a higher melting point?

Xe cause it has stronger interactions between electrons which requires MORE energy to break those interactions.

are attractive forces referring to x or y axis?

y-axis because attractive forces are related to energy of system and energy of system is on y-axis for PE well

would Xe minimum be lower or higher than He

lower because Xe has stronger attractive forces so it needs more energy to break interaction

would Xe minimum be shifted left or right compared to He?

right because Xe atoms electrons come into contact quicker because their electron cloud is so large

does Xe or He have bigger atomic radius?

Xe cause its a bigger atom so the internuclear distant/nuclei further apart

is the attraction stronger between 2 He atoms or 2 H atoms?

2 H atoms

why is the attraction between 2 H atoms stronger

because they covalently bond

which PE well is deeper, He or H?

Hydrogen PE well cause interaction between atoms happens quicker and at shorter distance; interaction much stronger

what happens when a 3rd molecule is added to an H-H system?

energy is removed, and new species formed=H2

why is it hard to separate H2?

because they are chemically bonded which requires a lot of energy to overcome

which interaction is stronger: LDFs or Covalent Bonds?

covalent bonds cause they’re stronger

whats an intermolecular force?

forces that exist between particles/atoms

what are examples of intermolecular forces?

Van Der Waals and London Dispersion Forces

what are bonds between atoms?

they occur WITHIN a molecule, are permanent, and are stronger/harder to break

at what temp(K) does it take to break He?

4 kelvin cause LDFs are weak

what happens when you heat H2 ?

high temp=fast moving atoms—>increase total energy of H2 through collision

what temp(K) does it take to break H2?

6000 kelvin

what bond holds nuclei together within H2 molecule?

covalent bond

why do H2 molecules stick to other H2 molecules?

cause of LDF’s cause its a force thats BETWEEN molecules

what happens when you break chemical bonds?

you get an INPUT of ENERGY into system, ex. add thermal energy which increases KE and molecule collisions

what happens when you form chemical bonds?

you RELEASE ENERGY from system, ex. energy moved from the system to its surroundings

what does a molecule of H2 look like?

2 nuclei w/ shared electron cloud

what kinds of bonds/interactions are present for H2 in solid phase?

both covalent bonds and LDFs present cause bonds are within molecules and forces are between molecules

whats an intramolecular force?

force that holds atoms together WITHIN a molecule