Comprehensive Study Notes: Periodic Table Trends and Group Properties

Group 1: The Alkali Metals

• General Properties:

  • Group 1 of the Periodic Table is known specifically as the "alkali metals."

  • This group includes the elements lithium ($Li$), sodium ($Na$), and potassium ($K$).

  • These elements share several common properties and trends in physical and chemical behavior.

• Data and Physical Trends:

  • Atomic Number: Increases as you go down the group ($3 \rightarrow 11 \rightarrow 19$). This indicates the size of the atom is increasing.

  • Mass Number: Increases as you go down the group ($7 \rightarrow 23 \rightarrow 39$).

  • Melting Point Trend: Decreases as you go down the group.

    • Lithium ($Li$): $180\,\text{}^{\circ}\text{C}$

    • Sodium ($Na$): $98\,\text{}^{\circ}\text{C}$

    • Potassium ($K$): $63\,\text{}^{\circ}\text{C}$

    • Prediction for Rubidium ($Rb$): It is expected to have a melting point lower than $63\,\text{}^{\circ}\text{C}$.

  • Boiling Point Trend: Decreases as you go down the group.

    • Lithium ($Li$): $1360\,\text{}^{\circ}\text{C}$

    • Sodium ($Na$): $900\,\text{}^{\circ}\text{C}$

    • Potassium ($K$): $777\,\text{}^{\circ}\text{C}$

• Atomic Structure of Group 1 Metals:

  • The properties are similar because their atomic structures are similar; specifically, they all have one electron in their outermost shell.

  • Lithium ($Li$):

    • Atomic number: $3$; Mass number: $7$.

    • Components: $3$ protons, $3$ electrons, and $4$ neutrons.

    • Electronic Structure: $2,1$. (Two electrons in the first full shell, one electron in the second shell).

  • Sodium ($Na$):

    • Atomic number: $11$; Mass number: $23$.

    • Components: $11$ protons, $11$ electrons, and $12$ neutrons.

    • Electronic Structure: $2,8,1$. (First two shells are full, one electron in the third shell).

  • Potassium ($K$):

    • Atomic number: $19$; Mass number: $39$.

    • Components: $19$ protons, $19$ electrons, and $20$ neutrons.

    • Electronic Structure: $2,8,8,1$. (First three shells are full, one electron in the fourth shell).

Group 7: The Halogens

• General Properties:

  • Group 7 is known as the "halogens."

  • The group includes fluorine ($F$), chlorine ($Cl$), and bromine ($Br$).

  • These elements are non-metals.

  • States of Matter: Fluorine and chlorine are gases at room temperature; bromine is a liquid.

  • Reactivity Trend: Reactivity decreases as you go down the group. Fluorine is the most reactive, followed by chlorine, with bromine being the least reactive of the three.

• Data and Physical Trends:

  • Atomic Number: Increases down the group ($9 \rightarrow 17 \rightarrow 35$). Atomic size also increases down the group.

  • Color Trend: The colors darken as you go down the group.

    • Fluorine ($F$): Pale yellow.

    • Chlorine ($Cl$): Yellowish green.

    • Bromine ($Br$): Brown.

  • Melting and Boiling Point Trends: Both increase as you go down the group.

    • Fluorine ($F$): Melting Point $-220\,\text{}^{\circ}\text{C}$; Boiling Point $-188\,\text{}^{\circ}\text{C}$.

    • Chlorine ($Cl$): Melting Point $-101\,\text{}^{\circ}\text{C}$; Boiling Point $-34\,\text{}^{\circ}\text{C}$.

    • Bromine ($Br$): Melting Point $-7\,\text{}^{\circ}\text{C}$; Boiling Point $59\,\text{}^{\circ}\text{C}$.

• Atomic Structure of Halogens:

  • All halogens have seven electrons in their outermost shell, which defines their placement in Group 7.

  • Fluorine ($F$):

    • Atomic number: $9$; Mass number: $19$.

    • Components: $9$ protons, $9$ electrons, and $10$ neutrons.

    • Electronic Structure: $2,7$. (First shell is full with two, second shell has seven).

  • Chlorine ($Cl$):

    • Atomic number: $17$; Mass number: $35$.

    • Components: $17$ protons, $17$ electrons, and $18$ neutrons.

    • Electronic Structure: $2,8,7$. (First and second shells are full; third shell has seven).

  • Bromine ($Br$):

    • Mass number: $80$.

    • Atomic Number: $35$.

    • Predicted Electronic Structure: The outer shell will contain $7$ electrons.

Group 8: The Noble Gases

• General Properties:

  • Group 8 includes helium ($He$), neon ($Ne$), and argon ($Ar$).

  • Characteristics: They are all gases. They are inert (unreactive) and do not form compounds.

• Data and Physical Trends:

  • Melting Point Trend: Increases (becomes less negative) as you go down the group.

    • Neon ($Ne$): $-249\,\text{}^{\circ}\text{C}$.

    • Argon ($Ar$): $-189\,\text{}^{\circ}\text{C}$.

  • Boiling Point Trend: Increases as you go down the group.

    • Helium ($He$): $-269\,\text{}^{\circ}\text{C}$.

    • Neon ($Ne$): $-246\,\text{}^{\circ}\text{C}$.

    • Argon ($Ar$): $-186\,\text{}^{\circ}\text{C}$.

  • Atomic Size: Size increases as you go down the group.

• Atomic Structure of Noble Gases:

  • All elements in Group 8 have full electron shells, which accounts for their inert behavior.

  • Helium ($He$):

    • Atomic number: $2$; Mass number: $4$.

    • Components: $2$ protons, $2$ electrons, and $2$ neutrons.

    • Electronic Structure: $2$. (First shell is full).

  • Neon ($Ne$):

    • Atomic number: $10$; Mass number: $20$.

    • Components: $10$ protons, $10$ electrons, and $10$ neutrons.

    • Electronic Structure: $2,8$. (Both shells are full).

  • Argon ($Ar$):

    • Atomic number: $18$; Mass number: $40$.

    • Components: $18$ protons, $18$ electrons, and $22$ neutrons.

    • Electronic Structure: $2,8,8$. (All three shells are full).

Experimental Observation: Alkali Metals and Water

• Required Materials:

  • Safety equipment: Safety glasses (for students and teacher), large safety screen/screens to protect the entire class.

  • Apparatus: Large trough of water, white tile, scalpel or knife, long forceps.

  • Samples: Lithium, sodium, and potassium (stored in the normal way, typically in oil to prevent reaction with air/moisture).

• Methodology:

  1. The teacher demonstrates the reaction of each metal individually.

  2. A small piece of metal is cut on a white tile and placed into the water trough using long forceps.

  3. Observations are recorded for each metal's reaction.

• Reaction Implications:

  • The group name "alkali metals" stems from the fact that these metals react with water to form alkaline solutions.

  • The reaction becomes more vigorous as you go down the group (Lithium to Sodium to Potassium).

  • Rubidium ($Rb$) is not typically used in schools due to its extreme reactivity.

Questions & Discussion

• Where in the Periodic Table do you find the metals?

  • Metals are generally found on the left side and in the center of the Periodic Table.

• How many more electrons than lithium does sodium have?

  • Lithium has $3$ electrons and Sodium has $11$; therefore, sodium has $8$ more electrons.

• Group 7 Inquiries:

  • What happens to the size of atoms down the group? The size increases.

  • What is the structural similarity? They all have $7$ electrons in the outer shell.

  • Why is it called Group 7? Because of the $7$ outer-shell electrons.

  • Are halogens metals or non-metals? Non-metals.

  • Predicting Iodine ($I$): Being below Bromine ($Br$), Iodine would be expected to have higher melting and boiling points, a darker color, and be less reactive than Bromine.

• Group 8 Inquiries:

  • What trend is seen in melting points? They increase down the group.

  • What is the structural similarity? All have full outer electron shells.

  • Why is it called Group 8? Because the elements (excluding Helium) have $8$ electrons in their full outer shells.

  • Predicting Krypton ($Kr$): Krypton is expected to have a higher melting and boiling point than Argon ($Ar$) (closer to zero).

• Relationship between Atomic Structure and Periodic Table Position:

  • The number of electrons in the outer shell determines the group number.

  • The number of occupied electron shells determines the period (row) in which an element is located.

Summary Checklist

• The structure of the Periodic Table is directly related to the atomic structure (electron arrangement) of the elements.

• Elements in the same group possess similarities in their atomic structure (same number of outer-shell electrons) and differences (increasing number of total shells and protons/neutrons).

• The Periodic Table can be used as a tool to predict the structure and properties (such as reactivity, state, and melting point) of elements based on their position.