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Chemistry: Properties of Matter - The Periodic Table and Element Trends

Grade 8IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Periodic Table is arranged by increasing Atomic Number (ZZ), which represents the number of protons in the nucleus.

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Groups (vertical columns) contain elements with the same number of valence electrons, resulting in similar chemical properties.

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Periods (horizontal rows) indicate the number of occupied electron shells in an atom.

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Metals are located on the left and center of the table; they typically lose electrons to form positive cations (Mn+M^{n+}).

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Non-metals are located on the right side; they typically gain electrons to form negative anions (Xn−X^{n-}).

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Atomic Radius: Generally increases down a group (more shells) and decreases across a period from left to right (greater nuclear charge pulling electrons closer).

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Group 1 (Alkali Metals): Reactivity increases down the group because the valence electron is further from the nucleus (Li<Na<K<RbLi < Na < K < Rb).

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Group 17 (Halogens): Reactivity decreases down the group as it becomes harder to attract an incoming electron (F>Cl>Br>IF > Cl > Br > I).

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Group 18 (Noble Gases): Possess a full valence shell (e.g., 22 or 88 electrons), making them chemically inert/unreactive.

📐Formulae

A=Z+NA = Z + N

Net Charge=p+−e−\text{Net Charge} = p^+ - e^-

Max Electrons per Shell=2n2\text{Max Electrons per Shell} = 2n^2

Number of Neutrons(N)=Mass Number(A)−Atomic Number(Z)\text{Number of Neutrons} (N) = \text{Mass Number} (A) - \text{Atomic Number} (Z)

💡Examples

Problem 1:

An isotope of Phosphorus has an atomic number Z=15Z = 15 and a mass number A=31A = 31. Calculate the number of neutrons (NN) and provide the electronic configuration for a neutral Phosphorus atom.

Solution:

N=16N = 16; Electronic Configuration: 2,8,52, 8, 5.

Explanation:

The number of neutrons is found using N=A−Z=31−15=16N = A - Z = 31 - 15 = 16. For a neutral atom, electrons equal protons (1515). Following the 2,8,82, 8, 8 rule, the first shell holds 22, the second holds 88, and the remaining 55 go into the third shell.

Problem 2:

Magnesium (MgMg) is in Group 2. Predict the charge of a Magnesium ion and write its chemical symbol with the charge.

Solution:

Mg2+Mg^{2+}

Explanation:

Elements in Group 2 have 22 valence electrons. To achieve a stable full outer shell, Magnesium loses these 22 electrons. Since it loses two negative charges, the resulting ion has a charge of +2+2.

Problem 3:

Compare the atomic radius of Sodium (NaNa, Z=11Z=11) and Chlorine (ClCl, Z=17Z=17), both in Period 3.

Solution:

The atomic radius of NaNa is larger than the atomic radius of ClCl.

Explanation:

Both elements have electrons in three shells. However, Chlorine has more protons (1717) than Sodium (1111). This higher nuclear charge exerts a stronger pull on the electrons, drawing them closer to the nucleus and making the atom smaller.