exam 1

which statement best explains why atomic number (z) defines the identity of an element?

z equals the number of protons in the nucleus

for the nuclide 56_26Fe, how many neutrons are present?

30

A neutral atom has A =31 and Z=15. Which is the correct number of protons, neutrons, and electrons?

15p+, 16n0, 15e-

Two atoms are isotopes of the same element if they have:

the same atomic number but different numbers of neutrons

which change would convert a neutral atom into a different element?

add 1 proton

which statement correctly distinguishes mass number from atomic mass?

mass number is protons+ neutrons for one atom: atomic mass is the weighted isotope average

which best explains why isotopes usually have similar chemical behavior?

they have the same electron structure (z)

in rutherford’s gold-foil experiment, most alpha particles passed straight through. This implies atoms are mostly:

empty space

If an ion has z= 17 and a -1 charge, how many electrons does it have?

18

which subshell capacity set is correct?

s=2, p=6, d=10, f=14

what is the electron configuration of a neutral atom with 17 electrons (chlorine)

1s2 2s2 2p6 3s2 3p6

a neutral atom has configuration 1s2 2s2 2p6 3s2 3p4. How many valence electrons does it have?

6

which pair is most likely to show similar chemical properties because of periodic table position?

same group

what is a correct atomic radius trend statement?

radius increases down a group because electrons occupy higher shells

across a period (left—> right), atomic radius generally decreases primarily because:

nuclear charge increases, pulling electrons closer

an element has isotopes Y-63 (69.1%) and Y-65 (30.9%). What is the atomic mass?

63.6

which best matches the “periods” and “groups” definitions?

periods= rows; groups= columns

which conclusion is supported by the fact that only a few alpha particles were strongly deflected?

positive charge is concentrated in a tiny region

the configuration 1s2 2s2 2p6 3s2 3p2 corresponds to an atom with how many main-group valence electrons?

4

which statement is most consistent with the chapter summary?

isotopes differ in neutrons and affect atomic mass averages

a neutral atom has 16 electrons and mass number 34. What nuclide notation is consistent?

34_16S

which pair of nuclides are isotopes of the same element?

35-17Cl and 37_17Cl

what is the best reasoning chain explaining decreasing atomic radius across a period?

more protons—→ stronger attraction ——→ smaller radius

which best explains why He is an exception to the group-number valence shortcut?

helium’s outer shell is full with 2 electrons

which statement most precisely distinguishes mass number from atomic mass?

A is protons + neutrons for one isotope; atomic mass is weighted average of isotopes

if a neutral atom has Z= 13, which is its correct electron configuration?

1s2 2s2 2p6 3s2 3p1

which best supports the claim that most atomic mass is in the nucleus?

protons and neutrons are much heavier than electrons

two neutral atoms have the same Z but different A. Which must be different?

neutrons

what is the correct neutron count for 125_52Te?

73

a chloride ion (CI-) relative to neutral Cl has:

one more electron

which correctly identifies valence electrons?

electrons in highest occupied energy level

which situation would most likely change the atomic mass shown on the periodic table?

changing isotope abundances

which conclusion follows from Rutherford’s alpha particle results?

nucleus contains most mass

which group- valence match is correct?

16—→ 6

which best predicts Na —> Cl atomic radius trend across period?

decrease

which relationship among A, Z, and neutrons is correct?

n= A-Z

which configuration corresponds to 7 valence electrons (main group)?

…3s2 3p5

a neutral atom has Z= 29 and A= 63. How many neutrons?

34

which statement fits ordering by increasing atomic number?

ordered by protons

which change would NOT affect mass number A?

remove electron

which ion is most consistent with a Group 2 metal forming a stable ion?

Mg2+

which pair is isoelectronic (same number of electrons)?

Al3+ and Ne

which formula correctly balances charges for aluminum ion (Al 3+) and oxide ion (O2-)

Al2O3

what is the correct formula for calcium phosphate?

Ca3(PO4)2

what is the correct formula for ammonium sulfate?

(NH4)2SO4

which formula is written correctly using parentheses rules?

Ca3(PO4)2

which name correctly matches FeCl3?

iron (III) chloride

which formula matches copper (I) nitrate?

CuNO3

which correctly matches Na2CO3

sodium carbonate

which formula matches sodium sulfite

Na2SO3