Question

Draw electron configurations for each of the following elements according to the Bohr model. Indicate which electrons are valence electrons. a. \(\mathrm{Li}\) b. \(\mathrm{C}\) c. \(\mathrm{F}\) d. P

Short answer

a. Li: 2 electrons in the first shell, 1 valence electron in the second shell. b. C: 2 electrons in the first shell, 4 valence electrons in the second shell. c. F: 2 electrons in the first shell, 7 valence electrons in the second shell. d. P: 2 electrons in the first shell, 8 in the second, 5 valence electrons in the third shell.

Step-by-step solution

Understanding the Bohr Model

The Bohr Model visualizes the atom as a small nucleus surrounded by electrons that orbit in circular paths called electron shells. Each shell can hold a certain number of electrons: the first shell can hold up to 2 electrons, the second shell up to 8 electrons, and so on. The outermost electrons are considered valence electrons.

Lithium (Li) Electron Configuration

Lithium has an atomic number of 3. According to the Bohr Model, the first 2 electrons will fill the first shell, and the remaining 1 electron will go into the second shell. This last electron is the valence electron for lithium.

Carbon (C) Electron Configuration

Carbon has an atomic number of 6. The first 2 electrons fill the first shell, with the remaining 4 electrons going into the second shell. These 4 electrons in the second shell are the valence electrons for carbon.

Fluorine (F) Electron Configuration

Fluorine has an atomic number of 9. Following the Bohr Model, the first shell is filled with 2 electrons and the next 7 electrons occupy the second shell. Out of these, the 7 electrons in the second shell are the valence electrons.

Phosphorus (P) Electron Configuration

Phosphorus has an atomic number of 15. In the Bohr Model, 2 electrons fill the first shell, 8 electrons fill the second shell, and the remaining 5 electrons will be in the third shell. These 5 electrons in the third shell are the valence electrons for phosphorus.

Key concepts

Valence Electrons

Valence electrons are the electrons that reside in the outermost electron shell of an atom in its ground state. They are crucial in determining how an element will react chemically with others, as they are the electrons involved in forming chemical bonds. For instance, in the Bohr model exercise, lithium (Li) has one valence electron in the second shell, carbon (C) has four valence electrons in the second shell, fluorine (F) has seven, and phosphorus (P) has five in the third shell.

Understanding the number of valence electrons an element has can also help predict the element's properties, such as electrical conductivity and melting point. Elements from the same group in the periodic table typically have the same number of valence electrons, which accounts for their similar chemical behavior. For students, knowing how to identify valence electrons is essential for understanding molecular structures and chemical reactions.

Electron Shells

Electron shells, also known as energy levels, are the orbits around an atom's nucleus where electrons are most likely to be found. According to the Bohr model, the first shell can hold up to two electrons, and subsequent shells can hold more, generally following the rule of 2n² where n is the shell number. The first shell is closest to the nucleus and has the lowest energy, while the farther a shell is, the higher its energy.

Electrons fill the shells starting from the innermost shell to the outer shells. Electron configurations, such as those determined in our exercise for lithium, carbon, fluorine, and phosphorus, illustrate how electrons are distributed among the shells. Understanding electron shells is crucial because the chemical properties of an atom largely depend on the distribution of electrons across these shells.

Atomic Number

The atomic number of an element, represented by the symbol Z, defines the number of protons found in the nucleus of an atom and consequently the number of electrons surrounding the nucleus, assuming the atom is neutral. The atomic number is a unique identifier for each chemical element and determines its position in the periodic table. From the exercise, lithium's atomic number is 3, carbon's is 6, fluorine's is 9, and phosphorus' is 15. These numbers inform us directly about the number of protons and electrons in a neutral atom of each element.

Furthermore, the atomic number is fundamental when determining electron configurations, as shown in the Bohr model exercise. By knowing the atomic number, a student can deduce how many electrons need to be placed in each electron shell to represent the atom's electron configuration accurately.