1 The Structure of Atoms and Ions Ions Mr. ShieldsRegents Chemistry U01 L03

2 Atomic Number 1. The number of protons an element has determines it’s ATOMIC NUMBER Every element has a unique atomic # 2. Therefore every element has a different number of protons This makes it different from every other element Mosley’s and Rutherford’s work explained the key role of Protons in defining an element.

3 Atomic Number When we write the atomic number it is written to the Left of the element symbol and at the bottom. Atomic no. 3

4 Mass Number An Atoms Mass Number is the sum of both Protons & Neutrons in the nucleus. Protons and neutrons have about the same mass For example Carbon’s Atomic No. = 6. So if Carbon also had 8 Neutrons it’s Mass Number would be? 6p + 8n = 14

5 Mass Number When we write the Mass Number it is written to the Left of the element symbol and at the top. Atomic Mass Number = 7

6 Atomic Charge If atoms are neutral but have Positive Protons In the nucleus then there must be one electron to balance the positive charge of each Proton Therefore the ATOMIC NUMBER not only indicates the number of PROTONS but ALSO the number of ELECTRONS +/- We know atoms must be electrically neutral. Why?

7 Notation 12 C 6 12 = no. of protons + neutrons. 6 = no. of protons. 6 = no. of protons. 12 – 6 = 6 neutrons How many neutrons in this atom?

8 Notation You might also see atomic mass designated as C-12 or O-17. The number following the symbol is the mass number - not the atomic number. You might also see atomic mass designated as C-12 or O-17. The number following the symbol is the mass number - not the atomic number. With this designation you would have to look up the atomic number since it’s not designated. With this designation you would have to look up the atomic number since it’s not designated.

9C N 7 Mass number = ? Atomic number = ? # of neutrons = ? # of electrons = ? Mass number = ? Atomic number = ? # of neutrons = ? # of electrons = ? Try these … How many electrons in U-238? How many electrons in U-238? 92 How many neutrons in U-238? 146

10 Ions Atoms can gain or lose Electrons Atoms can gain or lose Electrons This ability to gain or lose electrons determines how an element will react to form bonds This ability to gain or lose electrons determines how an element will react to form bonds After an element that gains or loses one OR MORE electrons it is called an ION After an element that gains or loses one OR MORE electrons it is called an ION - + -

11 Positive Ions Gaining or losing electrons does not affect the number of protons an element has Gaining or losing electrons does not affect the number of protons an element has When an atom loses an electron it becomes POSITIVE (+) When an atom loses an electron it becomes POSITIVE (+) A Positive Ion is called an Cation A Positive Ion is called an Cation Remember this as “C+ “ Remember this as “C+ “ Note: The number of Protons now exceeds the number of Electrons Note: The number of Protons now exceeds the number of Electrons

12 Positive Ions Charge is indicated in the Upper Right of the element symbol Charge is indicated in the Upper Right of the element symbol Include the Sign of the charge plus the magnitude Include the Sign of the charge plus the magnitude Ex. +2, +3 Ex. +2, +3 Exception: +1 is written only as a + with no number Exception: +1 is written only as a + with no numberExample: Na  Na + + 1e - (or Na - 1e -  Na + ) Na  Na + + 1e - (or Na - 1e -  Na + ) Cu  Cu e - Cu  Cu e -

13 Negative Ions When an atom GAINS an electron it becomes NEGATIVE When an atom GAINS an electron it becomes NEGATIVE This Ion is called a Anion This Ion is called a Anion Remember this as “ A- “ Remember this as “ A- “ The number of ELECTRONS now exceeds the number of protons The number of ELECTRONS now exceeds the number of protons As before charge is written in the upper right As before charge is written in the upper right Charge is now negative so the number is written with a “-” sign Charge is now negative so the number is written with a “-” sign Cl + 1e -  Cl - Cl + 1e -  Cl - S + 2e -  S -2 S + 2e -  S -2

14 Ions N + 3 e -  N -3 QUESTION (2): Nitrogen can gain three electrons. Write the chemical equation for the gain of these three electrons. QUESTION (2): Nitrogen can gain three electrons. Write the chemical equation for the gain of these three electrons. QUESTION (1): Write the chemical equation QUESTION (1): Write the chemical equation for the loss of 1 electron from the Rubidium atom? Rb  Rb e-

15 Putting it all together How many protons, neutrons, & electrons in each of the following: How many protons, neutrons, & electrons in each of the following: 23 Na S F p, 12 n, 10 e 16 p, 18 n, 18 e 9 p, 10 n, 10 e