Class 9 Chemistry Chapter 4: Periodic Table and Periodicity of Properties Flashcards

Flashcards covering key definitions, periodic trends, configurations, and properties from Class 9 Chemistry Chapter 4.

How many elements were known by the end of the 18th century?

23 elements.

How many total elements are recognized in the modern periodic table today according to the lecture?

118 elements.

What is the modern periodic table defined as?

A systematic arrangement of elements on the basis of their increasing atomic number (number of protons).

Who discovered the concept of atomic number in 1913?

Moseley.

What symbol represents the atomic number of an element?

$$Z$$

What does the Periodic Law state?

If elements are arranged in the order of their increasing atomic numbers, their physical and chemical properties repeat in a periodic manner.

What are the horizontal rows in the periodic table called?

Periods.

How many periods exist in the modern periodic table?

7 periods.

What are the vertical columns in the periodic table called?

Groups.

How many groups are there in the modern periodic table?

18 groups.

Which two elements are present in the 1st period?

Hydrogen and Helium.

Which element begins the 2nd period and what is its atomic number?

Lithium, with an atomic number of $3$.

Which periods are classified as short periods?

Periods 1, 2, and 3.

Which periods are classified as long periods?

Periods 4, 5, 6, and 7.

What does the abbreviation IUPAC stand for?

International Union of Pure and Applied Chemistry.

Why are elements within the same group referred to as a family?

Because elements in the same column share similar electronic configurations and matching physical and chemical properties.

How were groups designated in the traditional/old IUPAC system?

Using Roman numerals combined with letters A and B (such as 1A, 2A, 3B).

How are groups numbered in the modern IUPAC numbering system?

Sequentially from Group 1 to Group 18.

What are valence electrons?

The electrons present in the outermost energy shell of an atom.

What feature regarding electrons is shared by all elements in the same group?

They have the same number of valence electrons.

How many valence electrons do elements in Group 1 and Group 2 possess?

Group 1 elements have 1 valence electron, and Group 2 elements have 2 valence electrons.

How many valence electrons do elements in Group 13, Group 14, and Group 15 possess?

Group 13 elements have 3, Group 14 have 4, and Group 15 have 5 valence electrons.

How many valence electrons do elements in Group 16, Group 17, and Group 18 possess?

Group 16 elements have 6, Group 17 have 7, and Group 18 have 8 valence electrons.

What are Group A elements called in the traditional periodic classification?

Normal, representative, or main group elements.

What are Group B elements called in the traditional periodic classification?

Transition elements.

Into how many blocks is the periodic table divided based on subshell electron filling?

Four blocks: s, p, d, and f blocks.

What determines the block to which an element belongs?

The specific subshell (s, p, d, or f) into which its outermost/last electron enters.

Which groups comprise the s-block of the periodic table?

Group 1 and Group 2.

Which groups comprise the p-block of the periodic table?

Group 13 to Group 18.

Which groups comprise the d-block of the periodic table?

Group 3 to Group 12 (transition elements).

Where are the f-block elements positioned in the periodic table layout?

In two separate horizontal rows at the bottom of the main periodic table.

What is the specific group name for Group 1 elements?

Alkali metals.

What is the specific group name for Group 2 elements?

Alkaline earth metals.

Why are Group 2 elements termed alkaline earth metals?

Because they form alkaline solutions and are abundant in the Earth's crust.

What is the specific group name for Group 17 elements?

Halogens.

What is the specific group name for Group 18 elements?

Noble gases (or inert gases).

Why are noble gases generally chemically unreactive?

Because their outermost valence energy shell is completely filled, conferring maximum stability.

What does the atomic number ($Z$) represent in a neutral atom?

The total number of protons or electrons in the atom.

Which principle governs the order in which electronic orbitals are filled with electrons?

The Aufbau principle.

What is meant by electronic configuration?

The systematic arrangement of electrons in an atom's shells, subshells, and orbitals.

In what order are subshells filled according to the Aufbau principle?

In order of increasing energy level, from lowest energy to highest energy.

What is the maximum electron capacity of an s subshell?

2 electrons.

What is the maximum electron capacity of a p subshell?

6 electrons.

What is the maximum electron capacity of a d subshell?

10 electrons.

What is the maximum electron capacity of an f subshell?

14 electrons.

What is the standard electron filling sequence from 1s up to 4p?

$$1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \rightarrow 3d \rightarrow 4p$$

What is the full electronic configuration of Sodium ($Na$) with atomic number $Z = 11$?

$$1s^2\,2s^2\,2p^6\,3s^1$$

What is the block, period, and group of Sodium ($Na$) based on its electronic configuration $1s^2\,2s^2\,2p^6\,3s^1$?

Block = s, Period = 3, Group = 1.

What is the full electronic configuration of Aluminium ($Al$) with atomic number $Z = 13$?

$$1s^2\,2s^2\,2p^6\,3s^2\,3p^1$$

What is the block, period, and group of Aluminium ($Al$) based on its configuration $1s^2\,2s^2\,2p^6\,3s^2\,3p^1$?

Block = p, Period = 3, Group = 13 (or 3A).

What does the principal quantum number ($n$) represent?

The shell number or main energy level of an electron.

What letter names correspond to the first four electronic shells ($n = 1, 2, 3, 4$)?

K shell ($n=1$), L shell ($n=2$), M shell ($n=3$), and N shell ($n=4$).

Why do chemical elements undergo reactions and form chemical bonds?

To achieve a stable electronic configuration similar to nearby noble gases by completing their outer shell.

How many valence electrons constitute a stable octet for noble gases other than Helium?

8 valence electrons.

How many electrons constitute a stable duplet for Helium?

2 electrons.

What stable electronic configuration does Hydrogen attempt to attain when gaining an electron?

The Helium configuration ($1s^2$).

What type of ion is produced when a neutral atom loses electrons?

A positively charged cation.

What type of ion is produced when a neutral atom gains electrons?

A negatively charged anion.

What charge is typically acquired by Group 1 metals upon forming ions?

$+1$ charge (uni-positive cation).

What charge is typically acquired by Group 2 metals upon forming ions?

$+2$ charge.

What charge is typically acquired by Group 13 elements upon forming ions?

$+3$ charge.

What ionic charges can be shown by Group 14 elements?

$+4$ or $-4$ charges.

What charge is typically acquired by Group 15 non-metals upon forming ions?

$-3$ charge.

What charge is typically acquired by Group 16 elements upon forming ions?

$-2$ charge.

What charge is typically acquired by Group 17 halogens upon forming ions?

$-1$ charge (uni-negative anion).

What net charge resides on neutral noble gas atoms in Group 18?

$0$ charge.

According to chemical stability principles, what energy condition corresponds to maximum atomic stability?

The condition of minimum potential energy.

Which noble gas was found to form natural chemical compounds, challenging the view that noble gases are totally inert?

Krypton ($Kr$).

How does chemical reactivity change going down Group 1 alkali metals?

Reactivity increases down the group.

Why do Group 1 metals lose their valence electron more readily as you move down the group?

Because the valence electron is farther from the nucleus, experiencing weaker electrostatic attraction.

What products are formed when Sodium ($Na$) reacts with Water ($H_2O$)?

Sodium hydroxide ($NaOH$) and Hydrogen gas ($H_2$).

What atomic property primarily dictates the chemical behavior of an element?

Its valence shell electronic configuration.

What happens to the number of electron shells as you descend a group in the periodic table?

The number of shells increases by one with each consecutive period down the group.

How does the atomic number change as you move from left to right across a period?

It increases sequentially by $1$ unit from element to element.

What stays constant regarding inner shell electrons across a single period?

The total number of inner shell shielding electrons remains constant.

Define the shielding effect (screening effect).

The reduction in nuclear electrostatic force of attraction on outer valence electrons caused by the presence of inner shell electrons.

Which electrons are responsible for shielding valence electrons from the full attraction of the nucleus?

Inner shell electrons.

What is the trend of the shielding effect down a group from top to bottom?

The shielding effect increases down a group.

Why does the shielding effect increase down a group?

Because the number of inner electron shells increases.

What is the trend of the shielding effect across a period from left to right?

The shielding effect remains constant across a period.

Why does the shielding effect remain constant across a period?

Because new electrons enter the same outer shell while the inner shell electron count remains unchanged.

Between Beryllium ($Be$) and Magnesium ($Mg$), which atom has a greater shielding effect?

Magnesium ($Mg$) because it has more inner electron shells.

Define atomic radius (atomic size).

The average distance from the atomic nucleus to the outermost valence electron shell.

Why is it difficult to determine a sharp physical boundary for an isolated atom?

Because electrons move continuously in 3D probability density clouds without a fixed boundary.

How is the atomic radius practically determined experimentally?

By taking half of the distance ($\frac{d}{2}$) between the nuclei of two adjacent bonded identical atoms.

What is the trend of atomic radius across a period from left to right?

Atomic radius decreases across a period.

Why does atomic radius decrease from left to right across a period?

Because effective nuclear charge increases without adding new shells, pulling outer electrons closer to the nucleus.

What is the trend of atomic radius down a group from top to bottom?

Atomic radius increases down a group.

Why does atomic radius increase down a group?

Because new energy shells are added, placing outer electrons further from the nucleus.

Between Lithium ($Li$) and Sodium ($Na$), which has a larger atomic radius?

Sodium ($Na$) because it possesses three shells compared to two in Lithium.

Between Lithium ($Li$) and Beryllium ($Be$), which atom has a smaller atomic radius?

Beryllium ($Be$) because of its higher nuclear proton charge pulling the same shell tighter.

What is meant by effective nuclear charge ($Z_{eff}$)?

The net positive electrostatic charge experienced by a valence electron taking shielding into account.

What fundamental force attracts negative electrons toward the positive nucleus?

Electrostatic force of attraction.

How does an increase in distance between nucleus and valence shell affect electrostatic attraction?

It decreases electrostatic attraction according to the inverse square relationship ($F \propto \frac{1}{r^2}$).

Which subatomic particles increase in number in the nucleus across a period, increasing effective pull?

Protons.

Does the size of a neutral metal atom increase or decrease when it loses an electron to form a cation?

Decreases.

Why does atomic size shrink across a period despite adding electrons?

Because electrons enter the same shell while nuclear charge increases, enhancing total attraction.

What happens to the distance between nucleus and outer shell descending Group 1?

It increases significantly with each added shell.

What experimental measurement parameter is halved to obtain covalent radius?

The internuclear distance $d$ between two identical bonded atoms.

What formula calculates atomic radius $r$ from internuclear distance $d$?

$$r = \frac{d}{2}$$