Answer: Chemical decomposition

Why? Chemical decomposition is the breaking down of a molecule into smaller components and follows the general chemical equation AB → A + B. Decomposition is usually a result of environmental stimulation of some kind, for example heat, radiation, humidity and acidity. When carbonates (MCO₃, where M is any cation) are heated, they usually decompose to give carbon dioxide and a metal oxide. In the case of hydrogen carbonates, then water is also produced as a result.

Answering the Question:

To answer the question, it is important to pay special attention to the chemical equation. Of note is the addition of only heat and not another reactant. The equation then follows the general reaction AB + Heat → A + B.

2NaHCO₃(s) + Heat → Na₂CO₃(s) + H₂O(g) + CO₂(g)

AB + Heat → A + B

Answer: Magnesium and Barium are both members of the group 2 alkali earth metals of the periodic table.  This means they share many similar properties in terms of bonding and also have the same number of valence electrons. Magnesium has an electron structure of 1s² 2s² 2p⁶ 3s², this means that its outermost electron shell, the 3s shell has 2 electrons. Barium has an electron configuration of [Xe] 6s², meaning that in its outermost electron shell, 6s, it has 2 electrons. Therefore, both Mg and Ba have 2 electrons available for bonding, as a result of the 2 electrons in their valence orbitals.

Group two elements will try and achieve a noble gas configuration by donating the two valence electrons for chemical bonding and in aqueous solution form the ions Mg²⁺ and Ba²⁺.

Magnesium oxide (MgO) will dissociate to form Mg²⁺ and O^2-. As shown below;

MgO → Mg²⁺ + O^2-

The Lewis dot diagram of MgO would, therefore, be:

Answering the Question:

Answer: (4)

Why? The activity series of metals is a list of metal ions organized on the basis of the reactivity of the metals, usually with acids or water. It lists the metals from top to bottom, with the most reactive at the top and least reactive at the bottom of the table. The series provides a great deal of useful information, especially as it relates to the extraction of metals from their ores. Going from the bottom of the series to the top, a few trends are observed; 1) increase in reactivity, 2) more readily loses an electron to form a positive ion 3) corrode and tarnish more readily 4) requires more energy in order to separate them from their ores and 5) become stronger reducing agents.

Answering the Question:

Answer: (1)

Why? The general formula MCl shows the bond formed between a cation (positively charged ion) and Cl^- ion. Chlorine is a member of the chemical group called halogens. This group 17 element is typical of the group in that they have seven (7) valence electrons and would readily accept an electron to form ions of the general type Halogen^-1. Halogens will readily form compounds with metals, such as those found in group 1 and 2 of the periodic table.

Answering the Question:

A ood understanding of the periodic table is essential to answering this question. The general formula MCl has a ratio of 1M : 1Cl. It is safe to assume that the ion M could be written M⁺¹, since Cl will only accept one electron. Group 1 of the periodic table, alkali metals, will form ions with the general formula M⁺¹. It would stand to reason that M is a member of the group 1 metals. Analyzing each answer in turn: Answer (1) Rb or Rubidium, is a group 1 element, so it is a possible correct answer. Answer (2) Ra or Radium, is a group 2 element and will readily give up two electrons to form a Ra²⁺ ion. The resulting compound would have the chemical formula RaCl₂, which is not in agreement with the formula MCl. Answer (3) Re or Rhenium is a transition metal and as such has many oxidation states and hence many ions. However, most of the ionic states of Re are Re⁴⁺, Re⁵⁺ and Re⁶⁺ which would not be in agreement with the general formula MCl. Answer (4) Rn or Radon is a member of group 18 (noble gases), which tend to be very stable and will not react with most other elements.

Answer: 3

Why? Understanding the nature of the group of elements helps to know what kind of bond cobalt (Co) will form. Cobalt is a member of the transition metals and is a solid at standard temperature and pressure. The transition metals belong to groups 3 - 12 of the periodic table. They are unique in some of their properties mostly as a result of their d-sub shell electron arrangement. Transition metals have properties just like any other metal in that they have a high density, high melting points and boiling points; this is due to their metallic bonds. Cobalt is a metal, and therefore, its atoms will form metallic bonds with other metals.

Answering the Question:

Answer: 3 & 4

Why? To answer this question, we can use the process of elimination. The question is asking for two categories of compounds, firstly we need to understand what a compound is. A compound is any chemical species formed from two or more atoms chemically bonding together. The chemical bonds are covalent or ionic and are formed depending on the nature of the atoms and the conditions of the reaction that formed them.

Answering the Question:

Answer: 2

Why? It is important to have an understanding of what polarity is and how it occurs. When atoms of an element form a molecule, they share electrons. The electrons become distributed but are not always shared equally; this causes the formation of a dipole or areas of charge across the molecule. The other way in which a molecule will form a dipole is as a result of the molecule being asymmetrically arranged and causing polarity to occur. The attraction that an atom in a molecule has for electrons is termed electronegativity and is a measure of the attraction one atom has over another towards the electrons. If the electrons present on each atom are shared equally, then none of the atoms forming the molecule will have a net charge present, resulting in the molecule being non-polar. If, however, one or more atoms in the molecule have a stronger affinity for the electrons, they will pull the electrons closer to their nuclei. This causes a net charge to develop around the molecule. At some point along the molecule, there will be a net negative charge and, at another, a net positive charge resulting in the creation of a dipole. The molecule is then said to be polar.

Answering the Question:

As a general rule, the following molecules are said to be polar:

(1)     Molecules that are linear (carbon monoxide)

(2)     Molecules that have a single hydrogen or hydroxide group at one end

(3)     Molecules with an oxygen at one end

(4)     Molecules with a nitrogen at one end

On the other hand, diatomic molecules and most carbon compounds tend to be non-polar.

Answer: 4

Why? The periodic table of elements has many trends as you move across or down. As you move down any groups of the periodic table, the atoms of the elements will become larger. However, as you move across the period, from left to right, the atoms of the elements will become smaller. The decrease in size as you move across the period is a result of the increased forces of attraction between the nucleus and the orbiting electrons. As you move across the periodic table, the number of protons, and hence electrons, increases. This increase is responsible for greater forces of attraction and, hence, a reduction in the distance of the outermost electrons from the nucleus.

Answering the Question: