5.1.1 The atom (3)
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1.
Describe how the scattering of alpha (α) particles by a sheet of thin metal supports the nuclear model of the atom, by providing evidence for: (c) a nucleus that is positively charged
The positive charge of the nucleus is evidenced by the electrostatic repulsion between the positively charged alpha particles and the positively charged protons within the nucleus. As alpha particles approach the nucleus, they experience a strong electrostatic force that causes them to deflect. The direction and magnitude of the deflection are directly related to the strength of the electrostatic force. The fact that the alpha particles are deflected, and often change direction significantly, indicates that they are interacting with a positive charge. This repulsion is consistent with the model of a positively charged nucleus.
- The deflection of alpha particles demonstrates the presence of a repulsive electrostatic force.
- The direction of deflection is away from the nucleus, indicating a positive charge.
- The energy loss of alpha particles upon interaction is due to the electrostatic interactions.
2.
Atoms can form ions. Explain, in terms of the number of protons, electrons and neutrons, how a positively charged ion (cation) is formed. Include a diagram to illustrate your explanation.
A positively charged ion (cation) is formed when an atom loses one or more electrons. Atoms have a positive nucleus containing protons and a negative charge due to orbiting electrons. The number of protons in the nucleus defines the element. When an atom loses electrons, it has more protons than electrons, resulting in a net positive charge. The atom has become a cation. The number of electrons lost determines the charge of the ion. For example, if an atom loses one electron, it becomes a +1 ion (cation); if it loses two electrons, it becomes a +2 ion, and so on.
Diagram:
[Image missing: Ion Formation Diagram]
3.
State the components of an atom and describe the relative sizes and charges of each. Explain why the atom is generally electrically neutral.
An atom is composed of three main subatomic particles: protons, neutrons, and electrons.
- Protons: Located in the nucleus. They have a positive electrical charge (+1).
- Neutrons: Also located in the nucleus. They have no electrical charge (neutral).
- Electrons: Orbit the nucleus in specific energy levels or shells. They have a negative electrical charge (-1).
The atom is generally electrically neutral because it contains an equal number of protons and electrons. The positive charge of the protons in the nucleus is balanced by the negative charge of the electrons orbiting the nucleus. This equal and opposite charge results in a net charge of zero.