Chem chapter 2

Describe and explain experimental evidence for why light is a particle

photoelectric effect

J. J Thomson

plum pudding and thought atoms were composed of negatively charged electrons

What would happen to the electron when a hydrogen atom absorbs electromagnetic radiation (light)

As an electron absorbs light, the energy level increases. As photons absorb the attractive force, the attraction is broken between the nucleus and the electrons causing the electrons to move further from the nucleus.

Explain why (in general) the first ionization energy increases across the period.

Across the row, the effective nuclear charge increases and so the electrons are experiencing a greater attractive force. This is what causes the atomic radius to decrease. Because this attractive force is stronger for the electrons in Chlorine than those in Sodium, more energy is required to overcome that attraction and remove the electron from Chlorine than from Sodium.

Explain the production of an emission spectrum.

An electron in an n=1 state absorbs a photon of light. The electron moves to a higher energy level (excited state). The electron will emit a photon and move back to the ground state. The released photon has energy that corresponds to the wavelength of light observed in the emission spectrum.

Explain why the atomic radius decreases across the row in the periodic table. What causes a heavier atom (with more subatomic particles) to be smaller in size than a lighter atom?

As you read across the periodic table from left to right, the number of protons and electrons increases. The valence electrons are shielded from the full charge of the nucleus by the core electrons. However because the number of core electrons stays the same, the effective nuclear charge also increases across the row. This means that the valence electrons of Chlorine experience a greater attractive force due to greater effective nuclear charge than those of Sodium. This results in the electrons of Chlorine being held more closely and thus accounts for the atomic radius being smaller.

Molecular orbital bond model

Atomic orbitals combine to form en equal number of molecular orbital Each orbital can contain up to two electrons Electrons in bonding orbitals stabilize the system Electrons in anti bonding orbital make it less stable Electrons are delocalized

Valence Bond

Atomic orbitals overlap to form a bond The greater the overlap, the stronger the bond Each bond made up of 2 electrons Electrons are localized

Why nuclear fusion require such high energies but release high energy as well.

Because the reaction has to overcome the repulsive force of two positive charged nuclei. Then release this energy as the 2 nuclei become one because mass is lost during the reaction.

Why do bond form between atoms?

Because valence electrons are attracted to the nuclei of other atoms.

What factors affect the size of an atom?

Both the force of attraction between the protons in the nucleus and the surrounding electrons, and the repulsion between electrons play a role. Ultimately it is a balance between these forces that determines the size of the atom.

Why does quantized energy mean?

Electrons can only have certain energies and is not a continuous scale.

Explain why relative melting points and boiling points for a substance exist as a molecule (h2) and differ from those that exist as continuous extended network (diamonds)

Diamond is an extended network with 4 covalent bonds and for carbon to move you have to break all 4 covalent bonds, H2 molecules floating all over held together by LDF and when they are heated up they overcome the LDF

Make an evidence that light (electromagnetic radiation) is a wave.

Double split interference

WHy is the emission spectrum of hydrogen different than sodium?

Each element has its own amount of electrons on different energy levels as well as different frequency and wavelength.

How do ionization energies provide evidence for quantization of energies of electrons?

Each orbital requires a different amount of energy for an electron to be removed.

what are the characteristics to why something doesn't conduct electricity?

Electrons are located in bonds between atoms - not free to roam. There is a large "band gap" between the bonding and antibonding orbitals.

Diamonds characteristics

High mp Hard Brittle (breaks along planes) Translucent (lets light through) Does not conduct electricity

Graphites characteristics

High mp Soft Slippery Grey, shiny Conducts electricity

Draw an energy diagram to compare the possible electron transitions that would produce the red emission line at the left of the spectrum and the blue line at the far right of the diagram.

In the process in part a, 2 different wavelengths of light are emitted. One wavelength would correspond to n=2 n=1 and the other to n=3 n=1. The n=3 n=1 transition would yield a photon of higher energy than the n=2 n= 1 transition. The higher energy photon would (most likely) correspond to blue light. The lower energy photon would be the red light.

Evidence for why electromagnetic radiation is a particle

Photoelectric effect

Make a claim that light (electromagnetic radiation) is a wave.

Light is a wave

Predict the relative size of isoelectric atoms and ions of mg 2+ and 0-

Mg2+ is bigger cause it has more protons, despite their valence electrons being the same energy level.

Why hydrogen can form a covalent bond but helium can't?

Molecular orbital theory

Why atoms don't have macroscopic properties like melting and boiling points and color

Not one atom can show properties cause we don't know how it interacts with others, same with color.

Explain the force and energy changes that occur when 2 atoms approach each other and for a bond, also explain why a third body is needed to form a stable bond.

Potential energy decreases as atoms come together and increase when the electrons repel. Atoms attract each other because the proton is attracted to the electron. Third molecule is needed because when bonds break the energy goes to the third atom. When third atom hits, it takes some energy form bond- release energy break bond- add energy

Schrodinger

Quantum mechanics model behavior of waves

Similarities between molecular orbital bond model and valence bond model

Similar because start with atomic orbitals like s, p, d and combine them to make different kinds of orbitals

Explain why we use energy diagrams to illustrate electron transitions, rather than using a Bohr model of the atom.

The Bohr model only works for hydrogen and implies knowledge of both the energy and position of electrons within the atom. Since we cannot know both, we use energy diagrams. These diagrams show that an electron can absorb a photon of light and move to a higher energy level or release (emit) a photon light to move to a lower energy level. These energy levels are not circular orbits that Bohr proposed in his model of the atom.

Rutherford

gold foil experiment, existence of positive nucleus

What do you think happens to the atomic radius when an electron is removed from a neutral atom (for example when Na forms Na+)?

The atomic radius will decrease. For any atom, removing an electron will result in a decrease in the amount of repulsive force between electrons. This allows the electrons to be drawn closer to the nucleus and the atomic radius to decrease.

What do you think happens to the atomic radius when an electron is added to a neutral atom (for example if Cl added an electron to form Cl-)?

The atomic radius will increase. For both Cl and Cl- the effective nuclear charge is the same. Therefore, the valence electrons will experience the same amount of attractive force. However by adding an electron, the amount of repulsive force increases. With more repulsive force, the electrons will have to move further away from the nucleus to maintain the balance between attractive and repulsive forces. Therefore, the atomic radius will increase.

Why is energy required to remove an electron from an atom?

The electrons are attracted to the nucleus of the atom by the electrostatic force between the positively charged protons and the negative electrons. Therefore, to remove the electron, that attractive force must be overcome via the addition of energy.

Estimate the number of atoms in the universe as a function of time (big bang theory)

The number of atoms are increasing greatly and then as time goes on there is nuclear fusion which created elements and decreased the amount of atoms.

Reasoning for why electromagnetic radiation is a particle

The number of electrons ejected stays at 0 until the threshold number is met or goes above then the frequency is higher.

Estimate the number of elements in the universe as a function of time.

The number of elements initially increased at an exponential rate as atoms assembled to form the various initial element, but overtime the number leveled off as less and less new elements were created.

Explain why the wavelength of the neutron is relevant while the wavelength of the baseball is not.

The wavelength of the neutron is similar in size to the neutron while the wavelength of the baseball is much smaller than the size of the baseball making it unimportant (and unable to be measured).

Why are only valence (not core) electrons involved in bonding?

Valence are in the outer shells of the atom. These electrons have greater attraction to the nucleus. Valence electrons also require less energy than core.

Explain why the ionization energy increases as you go from left to right across the periodic table

When you move across the row, the number of protons increase but the number of core electrons stay the same. This causes the effective nuclear charge to increase meaning stronger attraction between its nucleus and electron and the size of the atoms decrease because it's pulled in tighter.

Why spectra are direct evidence for existence of quantized energy levels

absorption and emission spectra, need exact amount of energy for the electron to move from ground state to excited state.

Explain how and why different atoms emit different wavelengths of light

amount of energy they are absorbing and that depends on how much energy they will give

compare and contrast atomic emission and absorption spectra and how they arise

atomic emission and absorption are shown based on their energy level. Emission is black with light lines, absorption is light with dark spots.

explain the concept of effective nuclear charge and how it effects atomic radii and ionization energy

atoms with high effective nuclear charge hold onto their electrons tightly so more attractive protons and negative electrons, the closer the protons will be to the nucleus and the bigger the electron cloud will be.

explain on a molecular/atomic level why metals are shiny

because absorption of photons will promote electrons to higher energy levels, it immediately falls back down causing metal to shine

explain on a molecular/atomic level why metals conduct electricity

because of the bonding orbitals, and the electrons ability to move freely.

explain on a molecular/atomic level why metals are malleable and ductile

because the atoms can move with respect to one another.

Delocalized bonds

conduct electricity

Coulomb's law to explain the relative size of neutral atoms and ions

coulombs' law is like particles repel and unlike charges attract so attractive protons are attracted to negatively charged electrons.

What is the strongest bond or interaction that will form between two iodine atoms (I)?

covalent bonds

predict trends in atomic radii and ionization energies based on placement in the periodic table

decreases across increases down

Use spectra to identify the presence of elements

each element has its own emission spectrum. You can look at each spectra and identify which elements are present. When atoms absorb energy, its electrons jump to higher energy levels. Each jump corresponds to a particular wavelength of light.

Claim for why electromagnetic radiation is a particle

electromagnetic radiation is a particle

Contrast absorption, emission and photoelectric effect

electrons are ejected in photoelectric photoelectric is above or exact

Valence electrons

electrons on the outermost shells, higher in energy

Bohr

electrons were contained within quantized shells that orbit the nucleus

What is radioactive decay

emitting particles alpha (helium), beta (electron and positive electron) and gamma (photon, atom doesn't change)

What is nuclear fusion

fusing of 2 or more lighter atoms into a larger one

Ranks electromagnetic radiation in terms of energy (wavelength, frequency)

highest energy and frequency is gamma largest wavelength is radio

Describe the chain of events that led from the big band to the atoms that make up your body.

it got to hot for atoms to exist and then once it cooled down even more atoms appeared and then the only atom that could have fusion was hydrogen because of the proton and electron attraction and then form hydrogen together into large masses called stars and then you undergo fusion.

How is the blue line on the emission spectra created?

it is the light the element is giving off. As the energy is released, the light is given off resulting in the band of blue.

describe how ionization energy support the idea of quantized energy levels in atoms

it takes a specific amount of energy to remove exactly one electron from an atom. There is a quantized amount of energy needed to overcome the attractive force between the electron and nucleus.

What is the strongest bond or interaction that will form between two iodine molecules (I2)?

ldf

core electrons

low in energy, close to the nucleus within the closed shell

Compare absorption, emission and photoelectric effect

need light for excitation (electrons) exact frequency for excitation lights a particle

What color has the greatest wavelength?

red, highest frequency and short wavelength

What is nuclear fission

splitting of a larger atom into 2 or more

Describe experimental evidence for the wave nature of electrons (diffraction)

the bending of waves around obstacles and opening double split experiment not photons

What determines whether a bond/interaction is stable? Explain how temperature influences the stability

the higher the temperature, the less stable it will be. The depth of the potential energy well determines the stability

Explain why the existence of photons (quantized light energy) explains the photoelectric effect.

the photoelectric effect occurs when light shines on a metal plate and electrons are ejected creating a current. Their is a relationship between the wavelength of light used and the type of metal the plate is made of, whether or not electrons are ejected.

Describe the relationship between the frequency and wavelength and velocity of a wave.

wavelength=h/mv c=(wavelength)(frequency)

Make a reason that light (electromagnetic radiation) is a wave.

waves are multiplying from each slit meet "in phase" and "out of phase". When waves meet in phase constructive interference causing the wave intensity to increase. These are the bright places. Out of phase destructive interference cancel each other causing dark places.