Download Unit 2: Atoms and their Electrons

Unit 2: Atoms and their Electrons
Useful formula:
c = f
where c= 3.00 x 108 m/s
E = hf where h = 6.626 x 10-34 Js
1/ = Rh ( 1/n12 – 1/n22) where Rh = 1.097 x 107 m-1
 = h/mv
where m is mass in kg an v is velocity in m/s
Answer the following questions:
1.
What is the wavelength of light that has a frequency of 4.72 x 1014 s-1?
2.
Calculate the energy of light that has a frequency of 7.28 x 1014 s-1?
3.
What is the energy of a mole of photons with a wavelength of 1250
nm?
4.
How many photons of light with a wavelength of 601 nm are
required to produce a total energy of 251 J?
5.
Calculate the wavelength, frequency and energy of the spectral line
produced when an electron in a hydrogen atom goes from n=5 to
n=2
6.
What is the quantum number that describes the average distance of
an electron from the atoms nucleus?
7.
What is the number of unpaired electrons in a ground state oxygen
atom?
8.
Which type of subshell consists of a set of five equivalent orbitals?
What is the quantum number and its value for this type of orbital?
9.
State the Aufbau and Pauli Exclusion Principle, and Hund’s Rule.
10.
Write the electron configuration of Br.
11.
Write the electron configuration of Cu.
12.
Write the electron configuration of Fe3+.
13.
Write the electron configuration of N3-.
14.
Arrange the following list in order of decreasing first ionization
energy.
F
Br
Se
Te
Sb
15.
Arrange the following list in order of increasing atomic size. Explain
your reasoning.
P
K
S
Na
Cl
16.
Arrange the following list in order of decreasing size.
Ar
Cl1Ca2+
S2K+
17.
The first ionization energy of magnesium is 738 kJ/mol and its
second ionization
energy is 1450 kJ/mol. For sodium the first
ionization energy is 496 kJ/mol and its second ionization energy is
4560 kJ/mol. Explain why the second ionization energy for sodium
is nearly 10 times the first while for magnesium it is only about twice
the first.
18.
Write balanced chemical reactions for the following:
a) sodium with water
b) calcium with water
c) potassium with bromine
Answers:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
6.36 x 10-7 m
4.82 x 10-19 J
9.57 x 104 J/mol
7.58 x 1020 photons
= 4.34 x 10-7m , f = 6.91 x 1014 s-1 , E = 4.58 x 10-19 J
the principle quantum number n
2
d orbitals, l = 2
Aufbau means from bottom up – orbitals are filled from the lowest
energy level first and then up, Pauli Exclusion principle states that
no two electrons in an atom can have all four quantum numbers the
same, Hund’s rule states that electrons do not pair up to fill an
orbital in a sublevel until all orbitals in the same sublevel are half filled.
1s22s22p63s23p64s2 3d104p5
1s22s22p63s23p64s1 3d10
1s22s22p63s23p64s2 3d6
13.
14.
15.
16.
17.
18.
1s22s22p6
F > Br > Se > Te > Sb
Cl < S < P < Na < K . Sodium, phosphorus, sulfur and chlorine are all
in the same period, therefore they all have the same number of
shielding electrons and the effective nuclear charge increases
based on the number of protons in the nucleus, therefore the atomic
radius decreases from left to right across the period. Potassium is
larger than sodium because not only does the number of protons
increase but so do the number of shielding electrons as well as the
number of layers of shielding electrons, increasing the distance the
outer valence electrons are from the nucleus thereby making the
atom larger than sodium.
In this list all species contain 18 electrons, they are all isoelectronic
with Ar. Therefore the more positive the charge the smaller the ion
and the more negative the charge the larger the ion.
S2- > Cl1- > Ar > K+ > Ca2+
Removing a second electron from sodium requires breaking a noble
gas electron configuration. This configuration is extremely stable
as is demonstrated by the large amount of energy required to
remove the second electron from sodium. This is a 2p electron In
contrast magnesium reaches the noble gas configuration by
removal of the second electron which is 3s electron and takes less
energy to remove than the 2p electron in sodium. However this is
the second electron removed from the 3s orbital and it is more
difficult to remove than the first because there is no longer any
other valence electron repelling it.
a) 2Na (s) + H2O (l)  2NaOH (aq) + H2 (g)
Group 1 metals react with water to form a metal hydroxide and
hydrogen gas.
b) Ca (s) + 2H2O (l)  Ca(OH)2 + H2 (g)
Group 2 metals also react with water to form a metal oxide and
hydrogen gas.
c) 2 K (s) + Br2 (l)  2KBr (s) metal elements typically react with
non-metal elements to form binary ionic substances