Periodic Table eBook

The atomic number is the number of protons in an atom, which is unique for every element. It also equals the number of electrons, which decide the properties of an element. So, arranging by atomic number automatically places elements with similar properties into the same groups.

The word "periodic" means "repeating at regular intervals." In the periodic table, the properties of elements (like valency, reactivity) repeat after certain periods (rows). For example, every new period starts with a very reactive metal and ends with a noble gas.

As we move down a group, a new electron shell (energy level) is added with each period. These new shells are farther from the nucleus, making the atom larger.

Elements in the same group have the same number of valence electrons because their atoms have the same number of electrons in their outermost shell. For example, all elements in Group 1 (like Li, Na, K) have 1 valence electron.

No. Sodium (Na) is more reactive than calcium (Ca). Sodium has only 1 electron to lose to become stable, while calcium has to lose 2 electrons. It is harder to remove two electrons, making calcium less reactive than sodium.

Maximum atomic radius: Sodium (Na)
Minimum atomic radius: Chlorine (Cl) or Argon (Ar). (Sodium is largest, chlorine/argon is smallest in the third period).

Electronegativity is the ability to attract electrons. Elements in groups 16 and 17 (like O, F, Cl) have atoms that are just 1 or 2 electrons short of a stable octet. They have a very strong tendency to attract electrons to complete their outer shell.

It is easier to remove the first electron. After it is removed, the atom becomes a positive ion (Mg⁺). Now, the remaining electrons are held more tightly by the nucleus, making it much harder to remove the second electron.

No. Ionic bonds form when a metal gives electrons and a non-metal takes electrons. Two metals will both try to give electrons, and two non-metals will both try to take electrons. They form a different bond called a covalent bond.

Least Ionization Energy: Francium (Fr) or Cesium (Cs). These are the largest atoms where the electron is farthest from the nucleus and easiest to remove.

Highest Electron Affinity: Chlorine (Cl). It has a very strong desire to gain one electron to achieve a stable configuration.

We would place it in the periodic table based on its atomic number. The element would be put in a specific group and period where other elements have similar chemical properties. For example, if it has 1 valence electron, it would go in Group 1.

The first element is Hydrogen (H). It can both lose its single electron to form H⁺ (like a metal) or gain one electron to form H⁻ (like a non-metal), depending on the element it reacts with.

Aluminum (Al) will lose electrons more easily. A larger atomic radius (125 pm) means the outermost electrons are farther from the nucleus and are held less tightly, making them easier to remove.

The atomic radius is found by measuring the distance between the nuclei of two identical atoms that are bonded together and then halving that distance.

An oxygen atom already has 6 electrons. Gaining three electrons to form O³⁻ would mean having 9 electrons. This creates a very unstable ion with a high negative charge that is difficult to stabilize. Nitrogen, forming N³⁻, goes from 7 to 10 electrons, which is also difficult but is seen in some compounds like lithium nitride (Li₃N). For oxygen, the energy required to add three electrons is too high, so it prefers to gain only two electrons to form the stable O²⁻ ion (like in MgO).

If you don't know the atomic number, you need to know the element's chemical properties (like how it reacts, its valency) and its physical properties (like state, metallic character) to find which group it belongs to. Atomic mass is not very helpful for locating an element because the table is based on atomic number, not atomic mass. Some elements with higher atomic mass come before those with lower mass if their atomic number is lower (e.g., Argon (40) comes before Potassium (39)).

There are four main blocks: s-block, p-block, d-block, and f-block. Yes, these blocks are very helpful. Elements in the same block have electrons filling the same type of subshell (s, p, d, or f), which gives them similar properties. For example, all s-block elements are highly reactive metals.

A) Atomic radius:
Variation: Atomic radius decreases from left to right across a period.
Reason: As we move right, the number of protons (positive charge in the nucleus) increases. This stronger positive pull attracts the electron shells closer, making the atom smaller.

B) Ionization energy:
Variation: Ionization energy increases from left to right across a period.
Reason: Due to the decreasing atomic size, the outermost electrons are held more tightly by the nucleus. Therefore, more energy is required to remove an electron.

• State of Matter: Metals are usually solids (and conduct electricity), which hints at metallic bonding.
• Conductivity: Good conductors of heat and electricity are usually metals that form ionic or metallic bonds.
• Physical Appearance: Shiny, malleable substances are typically metals.
• The general rule: A metal + non-metal typically forms an ionic bond. Non-metal + non-metal typically forms a covalent bond.

1. Carbon (C)
2. Sulphur (S)
3. Phosphorus (P)
4. Iodine (I)

The number of elements in a period depends on how many electrons can fit in the available electron shells.

The 2nd period (n=2) can hold up to 8 electrons (2 in s-subshell + 6 in p-subshell).

The 3rd period (n=3) can also hold up to 8 electrons in its outermost shell (3s²3p⁶).

Hence, both have 8 elements. Later periods are longer because d and f subshells begin to fill, which can hold more electrons.

This statement is true. The benefits of the periodic table are:

1. Systematic Classification: It organized all known elements in a logical order based on their properties.
2. Predictive Power: It allowed scientists to predict the existence and properties of elements that had not yet been discovered (e.g., Gallium).
3. Relationship Revealed: It clearly shows the relationship between atomic structure and the chemical behavior of elements.
4. Easy Reference: It serves as a quick and easy guide to understand the trends in physical and chemical properties of elements.

The main reason is their exceptionally small atomic size.

• Lithium (Li): Its small size gives it a high charge density, making its compounds more covalent than ionic (like other Alkali Metals). For example, Li₃N is stable, while Na₃N is not.
• Beryllium (Be): Similarly, its small size and high charge density make its compounds covalent and amphoteric (can react with both acids and bases), unlike the purely basic oxides of other Alkaline Earth Metals.

Basis of Difference	Mendeleev's Periodic Table	Modern Periodic Table
Basis of Classification	Atomic Mass	Atomic Number
Position of Isotopes	Could not place them properly (same mass? different properties?)	Placed correctly (same atomic number? same position)
Position of Hydrogen	Had a confusing position	Still has a unique position but is placed in Group 1
Grouping of Elements	Some elements were grouped based on similar properties but had different electronic configurations.	Elements in the same group have the same number of valence electrons.