Periodic Elements

Class 9 | TN State Board Science

Key Concepts

Atomic Structure:

• An atom is the smallest unit of an element.
• It consists of a nucleus (protons and neutrons) and electrons orbiting the nucleus.
• Protons have a positive charge, neutrons have no charge, and electrons have a negative charge.

Periodic Table:

• The periodic table is a tabular arrangement of elements based on their atomic number.
• Elements are organized in rows called periods and columns called groups.
• Elements in the same group have similar chemical properties.
• Elements in the same period have the same number of electron shells.

Atomic Number (Z):

• The atomic number is the number of protons in an atom’s nucleus.
• It determines an element’s identity.
• Elements are arranged in the periodic table in order of increasing atomic number.

Atomic Mass (Atomic Weight):

• The atomic mass is the average mass of an element’s isotopes, taking into account their abundance.
• It is measured in atomic mass units (amu).

Valence Electrons:

• Valence electrons are the electrons in the outermost energy level (shell) of an atom.
• They play a crucial role in chemical reactions and bonding.
• Elements in the same group have the same number of valence electrons.

Chemical Bonding:

• Atoms bond to achieve a stable electron configuration.
• Types of bonding include covalent (sharing electrons), ionic (transferring electrons), and metallic (sea of electrons).

Periodic Trends:

• Atomic size generally increases down a group and decreases across a period.
• Ionization energy (energy needed to remove an electron) increases across a period and decreases down a group.
• Electronegativity (tendency to attract electrons) increases across a period and decreases down a group.

Noble Gases:

• Group 18 elements (Helium, Neon, Argon, etc.) are noble gases.
• They have a full valence electron shell, making them stable and unreactive.

Alkali Metals:

• Group 1 elements (Lithium, Sodium, Potassium, etc.) are alkali metals.
• They are highly reactive and have one valence electron.

Halogens:

• Group 17 elements (Fluorine, Chlorine, Bromine, Iodine, etc.) are halogens.
• They are highly reactive nonmetals and need one more electron to achieve a full valence shell.

Transition Metals:

• Groups 3-12 elements are transition metals.
• They have varying valence electrons and are often used in alloys.

Metals vs. Nonmetals:

• Metals are generally shiny, conductive, and malleable.
• Nonmetals are usually dull, poor conductors, and brittle.

Metalloids:

• Metalloids (e.g., Silicon, Boron) have properties between metals and nonmetals.
• They are often semiconductors.

Fill in the Blank Questions

Answer the following fill in the blank questions.

1. The __ is the smallest unit of an element.
2. Protons have a __ charge.
3. Elements in the same group have similar __ properties.
4. The atomic number of an element is the number of __ in its nucleus.
5. Elements are arranged in the periodic table in order of increasing __ number.
6. Valence electrons are found in the __ energy level of an atom.
7. Ionic bonding involves the __ of electrons.
8. The trend of atomic size generally __ across a period.
9. Noble gases have a __ valence electron shell.
10. Alkali metals are found in __ 1 of the periodic table.
11. Halogens are highly reactive nonmetals in __ 17.
12. Transition metals are typically found in __ 3-12.
13. Metals are good __ of heat and electricity.
14. Nonmetals are often __ conductors of electricity.
15. Metalloids have properties that are intermediate between __ and nonmetals.
16. The atomic mass of an element is measured in __.
17. Electronegativity increases __ a period.
18. The second period of the periodic table has __ energy levels.
19. __ is a noble gas used in balloons for buoyancy.
20. Boron is an example of a __.

Key

Verify your answers.

1. Atom
2. Positive
3. Chemical
4. Protons
5. Atomic
6. Outermost
7. Transfer
8. Decreases
9. Full
10. Group
11. Group
12. Groups
13. Conductors
14. Poor
15. Metals
16. Atomic mass units (amu)
17. Across
18. Two
19. Helium
20. Metalloid