To calculate protons, neutrons, and electrons, you need to use the atomic number and the mass number of the element. The atomic number is the number of protons in an atom, and it is usually written above the symbol of the element in the periodic table. The mass number is the sum of protons and neutrons in an atom, and it is usually written as a superscript before the symbol of the element. The number of electrons is equal to the number of protons in a neutral atom, but it can change if the atom has a charge. Here are some formulas to help you:
- Number of protons = atomic number
- Number of neutrons = mass number - atomic number
- Number of electrons = number of protons - charge (if the atom is positive) or number of protons + charge (if the atom is negative)
To draw a Bohr model for an element, you need to follow these steps:
- Draw a small circle in the center of the paper and write the symbol of the element inside it. This represents the nucleus of the atom.
- Draw concentric circles around the nucleus to represent the energy levels or shells of the atom. The first shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, the third shell can hold up to 18 electrons, and so on. You can use the formula 2n^2 to find the maximum number of electrons in each shell, where n is the shell number.
- Place dots or crosses on the shells to represent the electrons of the atom. Start from the innermost shell and fill it up before moving to the next shell. The outermost shell is called the valence shell, and the electrons in it are called the valence electrons. These electrons are important for chemical bonding and reactivity.
Here are some examples of how to calculate protons, neutrons, and electrons and draw a Bohr model for the elements you asked:
- Magnesium-25: The symbol for magnesium is Mg, and its atomic number is 12. Therefore, it has 12 protons. To find the number of neutrons, we subtract the atomic number from the mass number: 25 - 12 = 13. Therefore, it has 13 neutrons. Since magnesium is a neutral atom, it has the same number of electrons as protons: 12. Therefore, it has 12 electrons. To draw the Bohr model, we place 2 electrons in the first shell, 8 electrons in the second shell, and 2 electrons in the third shell.
```
25
Mg
12
o
o o
o o o o
o o o o o o
```
- Phosphorus-34: The symbol for phosphorus is P, and its atomic number is 15. Therefore, it has 15 protons. To find the number of neutrons, we subtract the atomic number from the mass number: 34 - 15 = 19. Therefore, it has 19 neutrons. Since phosphorus is a neutral atom, it has the same number of electrons as protons: 15. Therefore, it has 15 electrons. To draw the Bohr model, we place 2 electrons in the first shell, 8 electrons in the second shell, and 5 electrons in the third shell.
```
34
P
15
- Potassium-38: The symbol for potassium is K, and its atomic number is 19. Therefore, it has 19 protons. To find the number of neutrons, we subtract the atomic number from the mass number: 38 - 19 = 19. Therefore, it has 19 neutrons. Since potassium is a neutral atom, it has the same number of electrons as protons: 19. Therefore, it has 19 electrons. To draw the Bohr model, we place 2 electrons in the first shell, 8 electrons in the second shell, 8 electrons in the third shell, and 1 electron in the fourth shell.
```
38
K
19
```
- Oxygen-16: The symbol for oxygen is O, and its atomic number is 8. Therefore, it has 8 protons. To find the number of neutrons, we subtract the atomic number from the mass number: 16 - 8 = 8. Therefore, it has 8 neutrons. Since oxygen is a neutral atom, it has the same number of electrons as protons: 8. Therefore, it has 8 electrons. To draw the Bohr model, we place 2 electrons in the first shell and 6 electrons in the second shell.
```
16
O
8