Ch4: ATOMIC STRUCTURE AND PERIODIC TRENDS Flashcards
(97 cards)
1
Q
What is the smallest unit of any element?
A
One atom of the element
2
Q
What are the two components of the central nucleus of an atom? what are these known collectively as?
A
The protons and neutrons
Nucleons
3
Q
The electrons are held in the atom by what?
A
The electrostatic attraction of the positively charged nucleus
4
Q
What does the Z number represent?
A
The number of protons in the nucleus of an atom:
The atomic number Z
5
Q
What does the A number represent?
A
The atom’s mass number, A
The number of protons plus the number of neutrons in the nucleus
A= Z (protons) + N (Neutrons)
6
Q
What does the N number represent?
A
number of Neutrons
7
Q
What are the A, Z and N values of Beryllium- 9?
A
A: 9
N: 5
Z: 4
8
Q
What is an isotope?
Give example
A
When two atoms of the same element differ in their numbers of neutrons
ex. Beryllium- 7 and beryllium- 9
9
Q
What is the atomic weight of an element?
A
A weighted average of the masses of an elements naturally occurring isotopes
because elements exist naturally as a collection of their isotopes
This is the number represented on the periodic table below the sign
10
Q
What is an ion ?
A
When a neutral atom gains or loses electrons, it becomes charged and the resulting atom is called an ion
11
Q
What is a negatively charged ion?
A
An atom that has gained an electron (-1 unit)
Called an anion
12
Q
What is a positively charged ion?
A
An atom that has lost an election (+1 unit)
Called a cation
13
Q
What is the name of the force holding together protons and neutrons in a nucleus?
How does this force compare to the electrical force between charged particles?
A
Strong nuclear force
this force is stronger than the electrical force between charged particles: it has to overcome the repulsion that protons and protons have electrostatically (+) to keep the nucleus together
This is actually the most powerful force of the four fundamental forces of nature
14
Q
What are radioactive nuclei?
A
Unstable nuclei
They undergo Radioactive decay: a transformation to make them more stable altering the number and ratio of protons and neutrons or just lowering their energy
15
Q
What is radioactive decay?
What are the three types we discuss?
A
a transformation to make unstable/ radioactive nuclei more stable altering the number and ratio of protons and neutrons or just lowering their energy
Alpha, Beta, and Gamma
16
Q
What are unstable nuclei called?
A
Radioactive
17
Q
The nucleus that undergoes radioactive decay is known as the ____. The resulting more stable nucleus is known as the _____.
A
a) Parent
b) daughter
18
Q
What does it mean if a nucleus emits an alpha particle?
A
An alpha particle (4/2 α) consists of 2 protons and 2 neutrons
This is alpha decay: it reduces the parent atomic number by 2, and the mass number by 4
19
Q
What are the 3 types of Beta decay?
A
Beta- (most common)
Beta+
electron capture
20
Q
How do alpha particles act in environment?
A
they are emitted with high energy from parent nucleus but this energy quickly is lost as the particle travels through matter or air
THUS particles dont travel too far, and stopped by outer layers of human skin or piece of paper
21
Q
What is the name of the force that beta decay acts by?
A
Weak nuclear force
22
Q
How do beta particles act in the environment? Are they more or less dangerous than alpha?
A
more dangerous than alpha because they are much smaller —> more energy and greater penetrating ability
Can be stopped by aluminum foil or a centimeter of plastic or glass
23
Q
Which nuclei will undergo Beta- decay?
A
Those with too many neutrons
24
Q
Which nuclei will undergo Beta+ decay?
A
Those with too few neutrons
25
Which nuclei will undergo Electron capture?
Those with too few neutrons
electron capture is one process that unstable atoms can use to become more stable. During this, an electron in an atom's inner shell is drawn into the nucleus where it combines with a proton, forming a neutron and a neutrino. (the neutrino is ejected from the atom's nucleus). So those that will undergo it have too few neutrons and are wanting to make more to become more stable
26
What does it mean if a Beta- particle is emitted?
Beta particles (β) are high energy, high speed electrons (β-) or positrons (β+) that are ejected from the nucleus by some radionuclides during a form of radioactive decay called beta-decay. Beta-decay normally occurs in nuclei that have too many neutrons to achieve stability.
Conversion of a neutron into a proton and an electron (aka a B- particle)
Atomic number of daughter nucleus is 1 greater than the parent nucleus, but mass number remains the same
and 0/-1 B is ejected
ex. 14/6 C --> 14/7 N + 0/-1 B
27
What does it mean if a Beta+ particle is emitted?
Atomic number of daughter is 1 less than the parent nucleus, but mass number remains the same
conversion of proton into a neutron and a positron (0/+1B) which is ejected (this positron is the electrons antiparticle: identical to an electron except its charge is positive)
ex. 18/9 F ---> 18/8 O + 0/+1 B
28
What is electron capture?
An unstable nucleus increases its number of neutrons by capturing an electron from the closest electron shell and using it in conversion of a proton into a neutron
Atomic number of daughter is reduced by 1, and mass number remains same as parent (same as Beta+)
ex. 51/24 Cr + 0/-1e --> 51/23 V
29
What is Gamma Decay?
Simply an expulsion of energy
Brings an excited nucleus to a lower energy state
Doesnt change mass number or atomic number
ex. a/z X* ---> a/z X + 0/0γ
30
How do Gamma photons or Gamma rays act in the environment?
Have no mass no charge, very high energy and high frequency
Can penetrate matter effectively
few inches of lead or a meter of concrete will stop most gamma rays
31
What is a half life?
t 1/2
half life of a radioactive substance is the time it takes for one half of some sample of the substance to decay
The shorter the half life the faster the decay
32
What does the relationship of amount of radioactive substance to time look like?
The amount of a radioactive substance decreases exponentially with time
33
What is the equation for the exponential decay of radioactive substances?
N= No (1/2) ^ T/t 1/2
t 1/2= half life
T = total time sample has decayed
OR
N = No e ^ -kt
k= the decay constant
34
What is Nuclear binding energy?
The energy that was released when the individual nucleons (protons+neutrons) were bound together by the strong force to form the nucleus
equals the energy required to break up the intact nucleus into its individual nucleons
35
The greater the nuclear binding energy per nucleon... The more ____ the nucleus
stable
36
What is the mass defect?
Represents the binding energy
The difference between the total mass of the combined nucleus and the sum total mass of the separate nucleons individually
Δm = (total mass of separate nucleons) - (mass of nucleus)
37
What is the equation for the nuclear binding energy?
Eb= (Δm) c^2
c is the speed of light (3 x 10^8 m/s)
38
1 kg = ____ J
9 x 10^-16 J
39
1 amu= ~ _____ kg
1 atomic mass unit = ~ 1.66 x 10^ -27 kg
or =~ 1.66 x 10^-24 g
40
1 eV = ~ ___ J
1.6 x 10^ -19 J
41
Emission Spectrum
a spectrum of the frequencies of electromagnetic radiation emitted due to an electron making a transition from a higher energy state to a lower energy state
42
What is Plancks Constant
6.63 x 10^ -34 J . s
43
What is the equation for the energies of photons that are emitted by atoms?
E photon= hf = h c/λ
h is Plancks constant (6.63 x 10^-34 J.s)
c is the speed of light
44
Describe the Bohr Model of the Atom
- electrons in an atom orbit the nucleus in circular paths
- electrons with greater energy orbited nucleus at greater distances
- electrons have quantized energy states
- if an electron absorbs or loses energy exactly equal to the difference in energy between its current level and that of an available next level, it jumps to that one
45
How do you calculate the energies of the discrete energy levels given by bohr?
En= (-2.178 x 10^ -18 J) / n ^2
n is the energy level of the electron (eg. level n=1, 2, 3)
46
What are the criticisms of Bohrs atomic model?
- isn't good at predicting the atomic spectra of many electron atoms
- model cannot describe the electron- electron interactions that exist in many electron atoms
47
What is an orbital in the quantum model of the atom?
describes a three dimensional region around the nucleus in which the electron is most likely to be found
48
What are key characteristics of the quantum model of the atom?
- The energy shell (n) of an electron is same as circular orbits in Bohr model
- no longer describes the path of electrons around nucleus as circular orbits: orbital is a 3D region where electron is most likely found
- subshells: made up of one or more orbitals and denoted by letter (s, p, d, f) describes the shape and energy of the orbitals
- each energy shell has one or more subshells, and each higher energy shell contains one additional subshell
1s
2s, 2p
3s, 3p
4s, 4p, 3d
etc
- orbitals have different 3D orientations in space
s=1 orientation
p=3 orientation
49
What is Hunds rule?
Electrons in the same subshell occupy available orbitals singly before pairing up
50
What is the aufbau principle?
Electrons occupy the lowest energy orbitals available
electron subshells are filled in order of increasing energy
51
What is the Pauli Exclusion principle?
There can be no more than two electrons in any given orbital
52
What is the electron configuration for neon?
1s^2, 2s^2, 2p^6
53
Noble gases
last column of the periodic table
all have outer 8 electrons in filled subshells (complete octet)
54
What is a diamagnetic atom? how does it act around externally produced magnetic fields?
An atom that has all of its electrons spin-paired
must have an even number of electrons and have all of its occupied subshells filled
individual magnetic fields that they create cancel and leave no net magnetic field --> atom will be repelled by an external magnetic field
55
What is a paramagnetic atom? How does it act around externally produced magnetic fields?
if an atom's electrons are not all spin paired
these atoms are attracted into externally produced magnetic fields
56
Which elements have anomalous electron configurations leading them to "donate" electrons from s orbital to d orbital?
A number of elements with a d subshell
Often to complete a half filled (5) or a filled (10) d subshell
Ex: Chromium, copper, Molybdenum, silver, gold , others in the same family (column)
57
What does it mean if two atoms are isoelectronic?
atoms or ions that have the same number of electrons and therefore the same electron configuration
58
Transition metals
Elements in the d block
59
Alkali metals
Group 1
60
Alkaline earth metals
Group II
61
Halogens
Group VII
62
Noble gases
Group VIII
63
Rare earth metals
The F block
64
What do we call the horizontal rows in periodic table?
period
65
What do we call each vertical column in periodic table?
Group or Family
66
Which elements are metalloids? (periodic table)
[B]
[Si]
[Ge] [As]
[Sb] [Te]
[Po]
67
What is nuclear shielding or the Shielding effect?
The masking and weakening of electrostatic attraction between the nucleus and outer electrons by inner electrons
68
How does the atomic and ionic radius trend across the periodic table?
Moving left to right across a period, atomic radius decreases
- d/t adding of electrons but no new shells, more tightly bound to atom from greater effective nuclear charge
As you progress down a group, atomic radius increases
- due to increased shielding
Radius decreases as electrons are removed
- ones left are drawn in more closely to nucleus
Radius increases as electrons are added
X+ < X < X-
69
What is first ionization energy?
IE or IE1: The amount of energy necessary to remove the least tightly bound electron from an isolated atom
70
What is second ionization energy?
The energy required to remove the least tightly bound electron from the cation X+ (already has 1 electron removed)
IE2 will always be greater than IE1
71
How does IE trend across the periodic table ?
As you move left to right across a period IE increases
As you move up a group, IE increases
Because as you move left to right and down to up, the valence electrons are more tightly bound
Ionization for any atom with noble gas configuration will always be very large
72
What is electron affinity?
The energy associated with the addition of an electron to an isolated atom
eg. if energy is released when an electron is added, the electron affinity is negative. Halogens have very large negative EA because another electron gives it a much desired octet configuration
If energy is required in order to add the electron, EA is positive. For ex, halogens and alkaline earth metals have positive EAs because the added electron begins to fill a new level
73
How does electron Affinity trend across a periodic table?
as you move left to right typically becomes more negative
moving up a group (except noble gases) EA typically more negative
but there are exceptions
74
What is electronegativity?
a measure of an atoms ability to pull electrons to itself when it forms a covalent bond
The greater the tendency to attract electrons, the greater the atom's electronegativity
75
How does electronegativity trend across the periodic table ?
typically similar to Ionization energy
Moving left to right, electronegativity increases
Moving down a group, electronegativity decreases
76
What is the order of electronegativity for the nine most electronegative elements?
F > O > N ~ Cl > Br > I > S > C ~ H
77
What is acidity?
A measure of how well a compound donates protons, accepts electrons, or lowers pH in a chemical system
78
Binary Acid
AN acid consisting of one hydrogen and one other non metallic element
structure HX
can dissociate in water : HX--> H+ + X-
79
How does acidity trend across the periodic table?
The more electronegative the element bearing the negative charge is, the more stable the anion will be
therefore acidity increases from left to right across a period
Acidity increases down a group- Vertical trend depends on the size of the anion :
- the larger the anion the more the negative charge can be delocalized and stabilized
80
An atom with 7 neutrons and a mass number of 12 is an isotope of what element?
Boron
81
Which of the following is NOT an example of a bohr atom?
a) H
b) He+
c) Li^2+
d) H+
H+ has a positive charge from losing the one electron in the neutral atom thereby having no electrons
Bohr atom is one that contains only one electron
82
What is the max number of electrons that can go into any s subshell? Any p subshell? Any d? any f?
s subshell has only one possible orbital orientation. only 2 electrons can fill any given orbital so s can hold 1x2= 2 electrons
p has 3 orientations. Can hold 3x2=6 electrons
d has 5 orientations. can hold 5x2=10 electrons
f has 7 orientations. Can hold 7x2=14 electrons
83
Which of the following could describe an ion with the same electron configuration as a noble gas?
a) An alkali metal that has gained an electron
b) A halogen that has lost an electron
c) A transition metal that has gained an electron
d) An Alkaline earth metal that has lost 2 electrons
Choice D
84
Of the following, the element that possesses properties of both metals and nonmetals is:
a) Si
b) Al
c) Zn
d) Hg
A because elements that posses qualities of both metals and nonmetals are called metalloids.
85
metalloids
elements that possess qualities of both metals and nonmetals
86
The electrons in a solitary He atom are under the influence of two forces, one attractive and one repulsive. What are these forces?
Electrostatic attraction between electrons and nuclear protons and electrostatic repulsion between the electrons
87
Compared to calcium, beryllium should have :
a) greater electronegativity and ionization energy
b) Smaller electronegativity and ionization energy
c) greater electronegativity and smaller ionization energy
d) smaller electronegativity and larger ionization energy
A: beryllium is higher in the column so it should have higher ionization energy and greater electronegativity
88
Of the following, which has the most negative electron affinity?
a) barium
b) bromine
c) Phosphorus
d) Chlorine
D:
89
Of the following, which has the smallest atomic radius?
a) Sodium
b) Oxygen
c) calcium
d) silicon
B
90
Of of the following, which is the strongest acid?
a) H2O
b) H2S
c) HCl
d) HBr
D
For binary acids, acidity increases with increasing stability of conjugate base
- those that are more electronegative are more stable, and chloride is more electronegative than sulfide so B eliminated
And when comparing anions in a fam, larger ones are more stable so A and C eliminated
91
Which atom has 3 unpaired electrons in its valence energy level?
a) Li
b) Be
c) C
d) N
D
92
Which of the following elements would be most strongly attracted to a magnetic field?
a) Mg
b) Ca
c) Cr
d) Zn
C
93
Which of the following colours would appear as a bright band in an emission spectrum of a yellow sodium vapor lamp ?
a) Yellow, indicating lesser wavelength than ultraviolet light
b) yellow, indicating a greater wavelength than ultraviolet light
c) Blue, indicating a lesser wavelength than ultraviolet light
d) Blue, indicating a greater wavelength than ultraviolet light
B: all visible light has greater wavelength than UV
94
Which of the following atoms/ions has electrons in the subshell of highest energy?
a) Cl-
b) Ca^2+
c) Cr+
d) As
D
95
Of the following metallic elements, which has the lowest second ionization energy?
a) Na
b) K
c) Mg
d) Ca
D
96
Which of the following has the smallest atomic or ionic radius?
a) Cl-
b) Ar
c) K+
d) Ca^2+
D
97
Metallic character results from an elements ability to lose electrons. On the periodic table it is expected that metallic character increases:
a) from left to right because the decrease in electronegativity would make it easier to lose electrons
b) From left to right, because the decrease in atomic radius would result in more stable positive ions
c) From left to right because the decrease in ionization energy would make it easier to lose electrons
d) From right to left because the decrease in electron affinity would result in more stable positive ions
C: because ionization energy, or energy required to remove electrons, decreases from right to left due to decrease in effective nuclear charge
