Practice
Atoms, Elements, and Compounds Exercise
Question 1: Define the following terms: a) Atom b) Element c) Compound
Answer 1: a) Atom: The smallest unit of an element that retains the properties of that element. It
consists of a nucleus containing protons and neutrons, surrounded by electrons. b) Element: A pure
substance made up of only one type of atom. It cannot be broken down into simpler substances by
chemical means. c) Compound: A substance formed when two or more different elements
chemically combine in fixed proportions. Compounds have different properties from their
constituent elements.
Question 2: Draw and label a simple diagram of an atom, including the nucleus, protons, neutrons,
and electrons.
Answer 2: This answer requires a diagram. Below is a textual representation.
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Nucleus: Central part of the atom containing protons and neutrons.
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Protons: Positively charged particles inside the nucleus.
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Neutrons: Neutral particles inside the nucleus.
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Electrons: Negatively charged particles orbiting the nucleus in shells.
Question 3: Explain the difference between a molecule and a compound with examples.
Answer 3: A molecule is a group of two or more atoms held together by covalent bonds. Molecules
can consist of the same or different elements. For example, O2 (oxygen gas) is a molecule made of
two oxygen atoms.
A compound is a substance made of atoms of different elements chemically bonded together. For
example, H2O (water) is a compound made of two hydrogen atoms and one oxygen atom.
Question 4: Describe how the periodic table is organized, including the significance of groups and
periods.
Answer 4: The periodic table is organized into rows called periods and columns called groups.
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Periods: Horizontal rows that indicate the number of electron shells in the atoms of the
elements.
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Groups: Vertical columns that contain elements with similar chemical properties due to
having the same number of electrons in their outermost shell.
Question 5: Write the chemical formula for the following compounds: a) Sodium chloride b) Carbon
dioxide c) Magnesium oxide
Answer 5: a) Sodium chloride: NaCl b) Carbon dioxide: CO2 c) Magnesium oxide: MgO
Question 6: Balance the following chemical equation:
H2+O2→H2O\text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O}H2+O2→H2O
Answer 6: The balanced equation is:
2H2+O2→2H2O2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}2H2+O2→2H2O
Question 7: Differentiate between ionic and covalent bonds with examples.
Practice
Answer 7:
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Ionic bonds: Formed when one atom transfers electrons to another atom, resulting in
positively and negatively charged ions that attract each other. Example: NaCl (sodium
chloride).
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Covalent bonds: Formed when two atoms share electrons to achieve a full outer shell.
Example: H2O (water).
Question 8: Describe the structure of a water molecule and explain why it is considered a polar
molecule.
Answer 8: A water molecule consists of two hydrogen atoms covalently bonded to one oxygen atom.
The oxygen atom has a higher electronegativity than hydrogen, causing the shared electrons to be
more attracted to the oxygen. This creates a partial negative charge on the oxygen and a partial
positive charge on the hydrogens, making water a polar molecule.