2. Atomic Structure & Periodic Trends Flashcards
What is the atomic number (Z)? What is the mass number (A)?
Z = the number of protons in the nucleus of an atom. A = mass number is the number of protons and neutrons (nucleons)
we usually refer to atoms by their mass number:
beryllium-9
t or f, isotopes have the same atomic number, but differing mass numbers.
true
an isotope is an atom with differing number of neutrons (therefore the mass number changes)
what is atomic weight?
elements exist naturally as a collection of their isotopes. Atomic weight is a weighted average of these isotopes based on their prevalence in nature.
what holds protons and neutrons together in the nucleus?
the strong nuclear force. It is the strongest force in nature but only acts over very small distances. (it must overcome proton-proton repulsion).
Explain Alpha decay.
large nuclei release 2 protons and 2 neutrons (alpha particle/helium) to become more stable. Alpha particles are high energy, but lose this energy fast and therefore stop quickly.
Our skin can stop alpha particles.
Explain Beta (-) decay.
an unstable nucleus converts a neutron into a proton and an electron. It then ejects that electron which is called the beta-(-) particle.
here, Z increases by one, A stays the same
Explain Beta(+) decay.
Also known as positron emission. An unstable nucleus converts a proton into a neutron and a positron. the positron (B+ particle) is emitted.
here, Z decreases by one, A stays the same
Explain Electron capture.
Here an atom captures an electron from its closest shell (n=1 shell) and uses it to convert a proton into a neutron.
Here, the Z decreases by one, A stays the same.
What form of beta decay is the most common?
Beta (-) decay is the most common. if not specified, beta (-) decay is default.
Explain gamma decay.
When an excited atom (often one that has previously undergone alpha or beta decay) ejects a gamma photon. This photon has no mass or charge but can travel very far with a lot of energy.
unlike alpha and beta decay, gamma decay does not change the atoms composition at all.
summarize how an atom’s composition changes for all 5 forms of radioactive decay.
alpha: loses 2 protons and 2 neutrons (A down by 4, Z down by 2)
B- : Z up by one (converts neutron to proton)
B+ : Z down by one (converts proton to neutron)
E capture: Z down by one (converts proton to neutron)
gamma: no change in composition.
What is the equation for the half-life of a radioactive substance?
N = No (1/2) ^ T/t
N = substance left No = starting mass T = time passed t = half life
Explain nuclear binding energy and the mass defect.
Nuclear binding energy = energy needed to split a nucleus apart.
When nucleons bind together to form a nucleus, some mass is converted to energy. The loss in mass is called the mass defect
Δm = (sum of all nucleons mass) - mass of nucleus
Emission spectrum: each element gives off a unique spectrum of light when current is passed through it. The energy of the photons released can be explained by what equation?
E = hf = h(c/λ)
h = planck’s constant = 6.6 x 10e-34 js
Bohr model of the atom. Explain absorption and emission of electrons.
Bohrs model explains quantized energy states that surround an atom. Electrons can only occupy these quantized states and nothing in-between.
Absorption: electrons can capture energy and get excited to an outer shell of an atom
Emission: electrons can release energy and fall down to a lower shell (lower energy shell).
due to this quantized nature, emission spectra is not continuous but rather a set of unique lines.
t or f, the distance an electron jumps or falls in the Bohr model is directly related to the energy absorbed or emitted.
true. if an electron jumps from ground state to n=4, that is more energy absorption than if it went to n=2
write the equation for the energy of the released photon when an electron falls from n=4 to n =2.
E = hf E = E2 - E4
hf = E2 - E4
With atoms that only contain one electron (H, He+m etc), we can use what formula to calculate the energy of a discrete energy level?
En = (-2.2 x 10e-18 J) / n^2
Therefore, we can use this formula to find the difference between energy levels
ΔE = E2 - E1 (substitute in above equation)
true or false, atoms with one proton are considered Bohr atoms.
false! Atoms with one electron (H Li 2+, etc) are Bohr atoms.
The quantum model of an atom. Explain
- the energy shell
- the energy subshell
- the energy shell (n): designates the discrete energy level an electron occupies
- the energy subshell (s,p,d,f): explains electron orbitals, most likely areas of electron density
What is diamagnetic and paramagnetic?
Diamagnetic: paired electrons in an electron orbital Paramagnetic: lone electron in an electron orbital. Paramagnetic atoms are attracted to magnetic fields (the lone electron wants a partner)
Electron configurations. Explain
- Aufbau principle
- Hunds rule
- Pauli exclusion principle
- Aufbau principle: Electrons occupy the lowest energy states first.
- Hunds rule: Electrons of the same subshell must occupy all subshell orbitals before pairing up. (e.g. p oribital has 3 orientations, one electron in each before pairing)
- Pauli exclusion principle: a maximum of 2 electrons can occupy one orbital at a time.
Why are noble gases non-reactive?
because they have a full valence shell (i.e. they complete the octet rule with their electron configuration).
t o f, diamagnetic atoms are attracted to magnetic fields
false, they are repelled (paramagnetic are attracted)
periodic table: what are periods what are families
period = row = horizontal family = group = column = vertical
electron configurations: what occurs when we get to the d-block?
the electron energy shell (n) that were are in is the period number - 1.
e.g. bromine
[Ar]-4s2-3d10-4p5
Note: for the f block we subtract 2 (won’t have to deal with this likely)
What major exception applies to filling out electron configurations?
d-block electrons prefer to be half fulled or entirely fulled (5 or 10 electrons). s orbital electrons can be promoted into the d-shell leaving 1 electron in the s shell.
t or f, atoms that gain an electron (anions) accommodate that electron in the lowest energy orbital possible.
true
What is isoelectronic?
isoelectronic indicates two atoms with the same electron configuration.
Neon and F- are isoelectronic
What happens if a transition metal loses an electron? How does the electron configuration change?
When electrons are ionized, they leave the highest energy shell (n) available. This means that transition metals lose their s shell electrons before their d shell electrons.
Ti+ –> [Ar]-4s1-3d2
What is the electron configuration of Cu+
transition metal promotes s electron in d shell
copper is [Ar]-4s1-3d10
Cu+ is [Ar]-3d10
since the largest energy shell loses its electrons first (n=4)
What is the difference between an excited state atom and an ion?
an ion has lost or gained electrons. An excited state atom is existing in a non-ideal electron configuration. For example oxygen 1s2-2s2-3p4 may exist as
1s2-2s2-3p3-4s1. an electron has become excited into the 4th energy shell
Explain why alkali and alkali earth metals are strong reducing agents while halogens are strong oxidizing agents?
alkali and alkali earth metals may lose 1 or 2 electrons, respectively, to obtain a full outer ring (which is stable). They really want to be oxidized making them strong reducing agents
halogens really want to be reduced to have 8 valence electrons. Therefore they are strong oxidizing agents. This is also why halogens naturally exist in a diatomic state.
What is electron shielding and effective nuclear charge?
the more electrons exist between the nucleus and the valence electrons, the more negative repulsion the valence electrons feel. This reduces the positive nuclear charge they feel giving an effective nuclear charge (Z-eff < Z)
What is ionization energy?
the amount of energy required to remove an electron from an atom. Note that first ionization energy is always the easiest. (IE1 < IE2)
What is electron affinity?
EA is how much an atom wants an electron. If an electron is added and energy is released (E is negative), than the addition was favorable.
What is electronegativity?
EN is a measure of an atoms ability to pull electrons towards itself in a covalent bond. FONClBrISCH
Explain acidity of atoms.
Acidity explains how likely an atom would give up a hydrogen (donates a proton) or accept electrons.
periodic trends: explain the trends of atomic radius ionization energy electron affinity electronegativity acidity
in increasing value
atomic radius –> bottom left (electron shielding and number of shells)
ionization energy –> top right (EN)
electron affinity –> top right
electronegativity –> top right
acidity –> bottom right (accepting electrons or donating protons: larger nuclei stabilize the negative charge better)
t or f, noble gases have very negative electron affinities.
False - despite the periodic trend (increasing top and to the right), noble gases do not want more electrons as they already satisfy the octet rule.
Note that exceptions can exist in periodic trends.
