Periodic Table Trends

Atomic Radius down Groups

Claim: Down a group, atomic radius increases (applicable for both group 1 and 17)
Evidence:
The radius of an atom is governed by two factors:

1.        The number of layers of electrons around the nucleus

2.        The attraction the outer electrons feel from the nucleus

Down a group, the only factor affecting the size of the atom is the number of layers of inner electrons which surround the atom, as more shells of electrons take up more space.

Every new period means an additional valence electron shell. We can compare two elements in group 1: Na and Cs. Na is in period 3, and has 3 electron shells; Cs is in period 6, and has 6 electron shells.
Reasoning
Reasoning: Atomic Radius is defined as the difference from the nucleus to an atom’s valence shell. Valence shells are the outermost shell of an atom. Since there are more electron shells between the valence shell and the nucleus, the distance between the valence shell and nucleus increases.

For example, the valence electrons in Cs are 3 more shells farther from the nucleus compared to the valence electrons in Na.

Electronegativity down groups

Claim: Down group 17/1, electronegativity decreases
Evidence: The positively charged nucleus of an atom attracts the negatively charged electrons around it.

As we go down a group, the number of valence electrons in the valence shell for each element is constant, but the number of electron shells increases. Therefore, the atomic radius for elements increases.

Reasoning: electronegativity is defined as the degree to which an element tends to gain electrons and form negative ions (anions) in chemical reactions

Since the negatively charged valence shell moves progressively farther from the positively charged nucleus as we go down groups, the force of attraction between the two is weaker. Thus, as we move down a group, it is harder for an element to attract more electrons and form anions

Reactivity for Group 1

Claim: Down a group, reactivity is increasing for metals

Evidence:

• According to the Octet rule, atoms in group 1 with 1 valence electron will tend to lose that electron to have a stable configuration.

• Reactivity has to do with how atoms gain/lose electrons to become stable, leading to it having a stable valence electron shell that aligns with the octet rule. The group 1 alkali metals will lose electrons and become cations.

• The atomic radius of electrons increases as we go down a shell

Reasoning

• the positively charged nucleus is where the negatively charged electrons are pulled to. Since the valence electrons are farther from the nucleus, there is less pull on the valence shell. Therefore, it will be easier for metals to lose their valence electron in a reaction, which is why reactivity increases as you go down the group for metals.

Reactivity for Group 17

According to the Octet rule, atoms in G17 with 7 valence electrons will tend to want to gain an electron to fill up their valence shell with 8 electrons.

Reactivity has to do with how atoms gain/lose electrons to become stable, leading to it having a full valence electron shell that aligns with the octet rule. Non-metals will gain electrons and become anions.
The atomic radius of electrons increases as we go down a shell.
Reasoning: The positively charged nucleus is where the negatively charged electrons are pulled to. Since the valence electrons are farther from the nucleus, there is less pull on the valence shell. Therefore, it will be harder for atoms to attract another electron to complete their valence shell; therefore reactivity decreases as you go down the group for nonmetals.

Melting/Boiling point for metals

Down a group, melting/boiling point decreases for metals

As you move down Group 1, the atomic size increases due to the addition of more electron shells. This increase in siez results in a greater distance between the nuclei and delocalized electrons. Because the attraction between the positively charged nuclei and negatively charged electrons decreases as the distance increases, the metallic bond between atoms decreases.

With weaker metallic bonds, less energy is required to break these bonds and transition from solid to liquid, or from liquid to gas. Therefore, both melting and boiling points decrease as you move down the group.

Melting/Boiling point for nonmetals

As you move down group 17, the atomic size increases due to the addition of more electron shells. This increase in electron shells leads to a larger atomic radius. Additionally, as the atoms get bigger, the molecules have more electrons (atomic number). More electrons means stronger intramolecular forces, making it harder to boil or melt them.

Atomic Radius across period 3

Claim: across period 3, atomic radius decreases

Evidence:

• across the period, the atomic number and number of protons are increasing

• the number of electrons are increasing but on the same shell

For example, Na has 11 protons, 11 electrons; Argon has 18 protons, 18 electrons.

Reasoning:

• Atomic Radius is defined as the total distance from the nucleus of an atom to the outermost orbital of its electron

• Protons have positive charge and attracts electrons. As a result, valence electrons are pulled closer to the nucleus

• For example, Ar has 7 more protons than Na but electrons remain on the same shell. Therefore, the valence electrons are pulled in closer to the nucleus, thus decreasing the distance between the nucleus and valence electrons, which is equal to the atomic radius.

Boiling/Melting point for Period 3

claim: For period 3, the boiling and melting point will increase until Silicon, and then decrease until Argon

• Silicon has the highest melting point

• Silicon is a metalloid, and has a “giant covalent structure”

• metals in group 1-3 have high melting points

• this is because they have metallic/ionic bonds

• nonmetals in group 5-7 have covalent bonds. G5 elements have triple bonds, G6 element have double bonds, and G7 elements have single bonds.

• Group 6 triple bonds are harder to break, hence it has a higher melting/boiling point than groups 6 and 7.

Electronegativity across period 3

Claim: across period 3, electronegativity increases

Evidence:

• across the period, the atomic number and number of protons are increasing

• the number of electrons are increasing but on the same shell

Reasoning:

• electronegativity is the degree to which an element tends to gain electrons and form negative ions in chemical reactions

• protons have positive charge and attracts electrons. Since all valence electrons are on the same shell, with more protons they are attracted more tightly to the nucleus. Therefore, as the number of protons increases, it is more likely the the element gains atoms in its valence shells due to a stronger attraction

• Additionally, according to the octet rule and periodic trends of reactivity, nonmetal elements on the right side of the table become more and more likely to attract electrons to fill up their valence shell, thus forming negative ions (anions).