Atom Composition Composition
Unknown atom X contains 37 protons and 48 neutrons.
Determine the atomic number, mass number, and identity of the atom. Use CER.
Atomic number: 37 (number of protons)
Mass number: 85 (protons + neutrons)
Identity: Rb, Rubidium (based on atomic number, found on periodic table)
Identify the atom in the pair (H, He) with the larger atomic radius?
H
H is smaller b/c it is further on the left side of the Periodic Table.
The further left an element is on the periodic table, the larger the atom is.
Identify the atom in the pair (H, He) that is more electronegative.
He
He is more electronegative b/c it is further right on the periodic table.
How many electrons can the first energy level or shell hold?
Second?
Third?
1st: 2 electrons
2nd: 8 electrons
3rd: 8 electrons
Define the Octet Rule.
Atoms are stable/happy when they have a full outermost energy level, usually at 8 valence electrons.
What is the procedure for determining the # of protons, neutrons, and electrons for an atom?
Protons: atomic number
Neutrons: mass number - atomic number
Electrons: atomic number - charge
Identify the atom in the pair (S,F) with the smaller atomic radius?
F
This is because F is further right on the periodic table than S is.
The further right an element is on the periodic table, the smaller the atom is.
Identify the atom in the pair (F, I) that is more electronegative.
F
F is more electronegative b/c it is further upwards than I on the periodic table.
Which of the following is true? Use CER:
a) A neutral argon atom has 18 valence electrons.
b) A neutral carbon atom has 4 valence electrons.
c) A neutral sodium atom has 11 valence electrons.
b) Neutral carbon atom has 6 total electrons, but it only has 4 valence electrons. The first two electrons fill the first shell/energy level, and the remaining fill the second shell.
Which groups of elements on the periodic table (1-8) are most likely to participate in a chemical reaction where the atoms lose electrons? Use an example to illustrate your point via CER.
Groups 1-3
Atoms participate in chemical reactions to fulfill the octet rule and become stable. It's easier for elements in groups 1-3 to lose electrons rather than to gain them. For example, it's easier for Li to lose 1 electron and become Li +1 rather than gain 7 electrons!
Which 2 atoms below are isotopes of one another? Use CER.
a) atom with 4 protons, 5 neutrons
b) atom with 5 protons, 4 neutrons
c) atom with 4 protons, 4 neutrons
a) and c) because they have the same number of protons (which determines the identity of the atom) but different number of neutrons (and thus different mass numbers). This fits the definition of isotopes: atom of the same element with different mass numbers.
Put the following (K, Fe, C, Ca) from largest to smallest atomic radius
K, C , Fe, Ca
C is further left of K, Fe is further left of C, Ca is further left of Ca.
The further left an element is on the periodic table, the larger the atom is.
Put the following (K, Fe, C, Ca) from least electronegative to most electronegative.
K, Ca, Fe, C
Reasoning: Ca is further right than K, Fe is further right than Ca, C is further right than Fe.
Which of the following 2 atoms have the same number of valence electrons? Use CER.
Cl
Li
B
F
F and Cl both have the same number of valence electrons because they are both in the same group in the periodic table. They are in group 7, so they each have 7 valence electrons.
Li has 1 valence electron because it is in group 1.
B has 3 valence electrons because it is in group 3.
Which groups of elements on the periodic table (1-8) are most likely to participate in a chemical reaction where the atoms gain electrons? Use an example to illustrate your point via CER.
Groups 5-8
Atoms participate in chemical reactions to fulfill the octet rule and become stable. It's easier for the elements in groups 5-8 to gain electrons rather than to lose them. For example, Chlorine has 7 valence electrons so it gains an electron to have 8 total and a charge of -1.
True or False:
Li atom (3 protons, mass number of 7) and Li atom (4 protons, mass number of 8) are isotopes of the same element.
Use CER.
False
Li atoms always have 3 protons because its atomic number is 3 and it determines the identity of the element. The second Li atom is actually a Beryllium atom due to its 4 protons. Isotopes change the number of neutrons and mass number, not the number of protons.
What is the trend for atomic radius that you see on the Periodic Table?
As you go right on the Periodic Table, the radii of the atoms decrease.
We learned the periodic trends, which state that the further left and further down an element is on the periodic table, the larger the atom is.
What is the trend for electronegativity on the Periodic Table and why does it occur (thinking about electron behavior in the atom, not just placement on the periodic table)?
Electronegativity increases going right on the Periodic table.
Electronegativity increases going upwards on the periodic table.
Draw the dot diagram for Florine. Use CER to explain your diagram.
Fluorine is in group 7, so it has 7 valence electrons. Dot diagrams only show the number of electrons in the outermost energy level.
True or False
To fulfill the octet rule, H must gain 7 electrons to fulfill the octet rule and have 8 total valence electrons.
False
H is an exception to the Octet Rule. The fundamental principle of the Octet Rule is that atoms want to be stable with a full outermost energy level. H loses an electron so it's first energy level isn't half empty.
Use <, >, or = to rank the size of the following. Use CER.
nucleus
neutrons
protons
atom
electrons
atom > nucleus > protons=neutrons > electrons
What is the trend for atomic radius on the Periodic Table and why does it occur?
As you go right on the Periodic Table, the radii decreases. Electrons are attracted to the protons (opposites attract), which are inside of the nucleus (in the center of the atom).
Elements lower on the the periodic table are larger b/c the mass number increases, which means more electrons for the atom.
What is the trend for electronegativity on the Periodic Table and why does it occur (thinking about electron behavior in the atom, not just placement on the periodic table)?
Elements on the right side and higher up on the periodic table are more electronegative.
Side-to-side: Atomic radius decreases as you go further right, so the distance for the electrons decreases as well. Elements on right side have more protons, which have a stronger pull on the atoms of the more left elements.
Up-Down: Atomic radius decreases as you go upwards, so the distance from the other atoms nucleus is smaller.
Draw the Dot diagrams for both H and He. Use CER to explain your diagram.
H is in group 1, so it has 1 valence electron.
He is in group 8, but it only has 2 electrons total, so it has 2 valence electrons (and not eight).
Which of the following elements is least likely to undergo a chemical reaction? Use CER.
Boron
Xenon
Oxygen
Potassium
Xenon because it's a noble gas and it's in group 8, meaning it has 8 valence electrons. Thus it has already fulfilled the octet rule and it's stable and does not need to chemically react.