Describe the properties of an atom.

• Atoms have internal structure.
• Atoms consist of a small, positively charged nucleus surrounded by one or more negatively charged electrons.
• The nucleus of an atom is made up of protons and neutrons.
• The number of neutrons and protons in an atom can be represented using nuclear notation.
• An ion is an atom with a nonzero net electric charge.
• Each atomic element has a unique number of protons.
• The number and arrangements of electrons affects how atoms interact.
• The total number of neutrons and protons identifies the isotope of an element.
• The mass of an atom is dominated by the total mass of the protons and neutrons in its nucleus.
• The Bohr model of the atom is based on classical physics and was the historical representation of the atom that led to the description of the hydrogen atom in terms of discrete energy states.
• In the Bohr model of the atom, electrons are modeled as moving around the nucleus in circular orbits determined by the electron’s charge and mass, as well as the electric force between the electron and the nucleus. Relevant equations:
• The standing wave model of electrons accounts for the existence of specific allowed energy states of an electron in an atom, because the electron orbit’s circumference must be an integer multiple of the electron’s de Broglie wavelength.

The analysis and description of electron structure is limited to energy levels and will not include such advanced descriptions as orbitals, orbital shapes, or probability functions.

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