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UCE (O-Level) Atomic combinations — practice questions

Explore 8 free Atomic combinations questions in UCE (O-Level) Chemistry. Open each question or exercise to read its content, reference answers and available explanation.

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Atomic combinations questions and exercises with answers

Showing questions 1–8 of 8.

How is a covalent bond between two atoms formed?Read the answer and worked solution →What name is given to the electrons in the outermost energy level of an atom?Read the answer and worked solution →An oxygen atom in a water molecule keeps two electron pairs entirely to itself. What are these pairs called?Read the answer and worked solution →In a dative covalent bond, where do the two shared electrons come from?Read the answer and worked solution →What does the electronegativity of an element measure?Read the answer and worked solution →According to VSEPR theory, how do the valence electron pairs around a central atom arrange themselves?Read the answer and worked solution →Bond energy is the amount of energy needed to do what?Read the answer and worked solution →A molecule has one end with a slightly positive charge and the other end with a slightly negative charge. What is it called?Read the answer and worked solution →

Worked practice questions

How is a covalent bond between two atoms formed?

  1. Sharing pairs of electrons
  2. Losing pairs of electrons
  3. Gaining pairs of protons
  4. Trading pairs of neutrons
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Correct answer: A. Sharing pairs of electrons

1. Atoms bond in order to fill their outermost energy level, as the noble gases already have. 2. A covalent bond is a chemical bond where pairs of electrons are shared between two atoms. 3. The outermost orbitals overlap so that unpaired electrons from each atom can be shared. 4. Protons and neutrons sit in the nucleus and take no part in ordinary bonding. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 3: Atomic combinations_

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What name is given to the electrons in the outermost energy level of an atom?

  1. Core electrons
  2. Valence electrons
  3. Bonded electrons
  4. Paired electrons
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Correct answer: B. Valence electrons

1. An atom has a central nucleus surrounded by electrons in fixed energy levels. 2. The electrons in the outermost energy level are called the valence electrons. 3. Only these electrons take part in bonding, which is why a Lewis diagram shows them alone. 4. Electrons in the inner levels are the core electrons, so that option names the wrong group. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 3: Atomic combinations_

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An oxygen atom in a water molecule keeps two electron pairs entirely to itself. What are these pairs called?

  1. A bond pair
  2. A free pair
  3. A lone pair
  4. A spare pair
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Correct answer: C. A lone pair

1. Oxygen forms one bond with each hydrogen atom using its two unpaired electrons. 2. The remaining two pairs are not shared with any other atom. 3. An unshared electron pair is called a lone pair, and it stays on the atom it belongs to. 4. A bonding pair is shared between two atoms, which is exactly what these pairs are not. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 3: Atomic combinations_

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