CHEM125 – REVIEW ACS I

REVIEW ACS I

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Question 1

How many atoms are in 2.17 g of Na? chem125-acs1 - Fluff Butt Reviews

Explanation

2.17 g Na/ (22.9898 g/ mol Na) = 0.09439 mol Na * (6.022*10^23) = 5.68 * 10^22 atoms

Question 2

Which statement concerning the structure of the atom is correct? Select one: chem125-acs1 - Fluff Butt Reviews CHEM125 - REVIEW ACS I 1

Question 3

What is the number of neutrons in the ion 80/35 Br-? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

80 (molar mass) Br – 35 (atomic #/ # of protons) 80 – 35 = 45 (# of neutrons)

Question 4

What is the expected empirical formula of gallium oxide? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

Gallium : Group 13 : Ga 3+ (2) Oxygen : Group 16 : O 2- (3) Its all about balance kiddos

Question 5

Which ion does not have 18 electrons? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

Sc 3+: 21e -3e = 18e Mn5+: 25e -5e = 20e K+: 19e-1e= 18e P3-: 15e+3e=18e one of these things is not like the other

Question 6

What is the maximum number of electrons that can occupy a px orbital? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

The MAX any orbital can hold is 2!!!!

Question 7

What is the valence electron configuration of the element in Period 4, Group 4A? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

lets be real this tripped me up for approximately ten minutes solely because i am apparently illiterate… the key word here is VALENCE as in only the outer shell so only level 4 energy levels should be included the element this question alludes to is Ge [ Period 4, Group 4a] and this element has a full 4s2 orbital and only 2 electrons in the p orbitals

Question 8

Four of the five d orbitals could be represented by Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

CHEM125 - REVIEW ACS I 2 s: spherical shape p: peanut shape d: double peanut shape

Question 9

For which of the following species does the Bohr model NOT work for determining the energy of an electron in an orbital? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

The Bohr model only works for elements and ions with 1 electron Extra Cool Stuff: This model depicts an atom as a solar system of sorts even though planets don’t circularly revolve around the sun, they go in a more elliptical fashion [ attraction is provided by electrostatic forces rather than gravity] Basically despite its extreme restrictions its still notable because of its success in explaining the Rydberg formula for the spectral emission lines of atomic hydrogen

Question 10

What is the electron configuration of Mn5+ in the ground state? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

According to the Aufbau principle electrons orbiting one or more atoms fill the lowest available energy levels before filling higher levels so 4s is filled before 3d, and one would assume when removed that 3d electron would be removed first but as per usual nothing is as it seems in chemistry apparently so the exact opposite occurs! And its not just because God is unjust and Butherus is coming after you personally but because as 3d fills up it’s energy levels decrease so 4s is removed first as it has the highest energy

Question 11

Which electron configuration is impossible? (Careful, excited states are possible.) Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

2d does not exist as a state or configuration

Question 12

How many unpaired electrons does Co2+ have? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

2 electrons are removed from the 4s level leaving the 3d level the same with 7 electrons and 3 unpaired electrons

Question 13

which of these species is paramagnetic? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

Remember the Mn5+ structure you probably drew or thought up earlier. it only has one unpaired electron, therefore it is paramagnetic

Question 14

Which of these diagrams could represent the ground state of the d valence electrons of V? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

Due to the Hund’s Rule and Pauli Exclusion principle it can’t be A or C. Basically electrons need to be spinning the same way, until they get partners that will spin the other way. And that electrons can’t be paired until every sub orbital is filled. And because V only has three electrons in the d level we are left with B.

Question 15

Which emission line in the hydrogen spectrum occurs at the longest wavelength? Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

Use the Rydberg formula: CHEM125 - REVIEW ACS I 3 CHEM125 - REVIEW ACS I 4 is the wavelength of the light emitted in vacuum; CHEM125 - REVIEW ACS I 5 is the Rydberg constant for this element; for H it’s 1.097373*10^7 m^-1 CHEM125 - REVIEW ACS I 6 is the atomic number CHEM125 - REVIEW ACS I 7 and CHEM125 - REVIEW ACS I 8, nCHEM125 - REVIEW ACS I 8 are integers such that nCHEM125 - REVIEW ACS I 10, corresponding to the principal quantum numbers of the orbitals occupied before and after. The smaller the energy emitted the longer the wavelength

Question 16

The element X occurs naturally to the extent of 72.25% 30X and the rest 32X. What is the atomic mass of X? (Use 4 sig. fig.) chem125-acs1 - Fluff Butt Reviews

Explanation

0.7225(30) + (1-0.7225)(32) = 30.55

Question 17

Which set of quantum numbers is correct and consistent with n = 3? (l = angular momentum quantum number, ml = magnetic q.n., and ms = electron spin q.n.) Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

n=3 –> principle quantum number (n) –> describes the size of the orbital [indirectly describes the energy of an orbital] l= 0,1,2 –> can be any integer between 0 and (n-1) ml: 0, -1<m<1, -2<m<2 –> any integer between -1 and l ms: +1/2 or -1/2 It can’t be A (ml) or C (l) or D (ms).

Question 18

Which element is represented by 33/11X?Select one: chem125-acs1 - Fluff Butt Reviews

Explanation

33 X 11 11 protons/ atomic # = Na (sodium)