Atomic Structure

Atomic Size Atom = Comes from Greek word for “uncuttable” or “indivisible” Smallest unit of an element that still maintains the properties of that element; Building blocks of matter Nucleus Electron Cloud

Each “circle” is an individual gold atom

- Basic Atomic Parts + Sub-atomic Particles Proton Neutron Electron Positively charged (+1) Mass = 1 atomic mass unit (amu) Found in nucleus of atom Neutron Neutrally charged (0) Mass = 1 amu Electron Negatively charged (-1) Mass ≈ 0 amu (is extremely small) Found in energy shells outside nucleus of atom + -

Basic Atomic Structure Nucleus Center of atom 99% of atomic mass in nucleus Where the protons and neutrons are found Electron Cloud (Energy Shells) Regions around nucleus where electrons are found based on how much energy they have Each shell can only have specific number of electrons N = 1 shell Can hold 2 electrons N = 2 shell Can hold 8 electrons N = 3 shell Can hold 18 electrons N = 3 N = 2 N = 1 Nucleus

_ N = 3 _ N = 2 _ _ _ _ N = 1 Nucleus + _ _ _ + _ _ _ + _ _ _ _ _ _

5 Things to Always Look For 2 electrons (2-) 8 electrons (8-) Type of Element Look at chemical symbol 1st letter always capitalized; 2nd letter always lower case Atomic Number (Z) It equals the # of protons Mass Number (A) (# of protons) + (# of neutrons) Everything in the nucleus Charge on Particle (# of protons) – (# of electrons) Atom or Ion? If charge = 0… it is an atom If charge ≠ 0… it is an ion 2 electrons (2-) 12 protons (12+) 12 neutrons (0) 12 Mg 2+ 24 -

Understanding Chemical Symbols Atomic Number (Z) Mass Number (A) Element? Oxygen How many protons? Same as atomic number (Z) = 8 protons How many neutrons? Mass number – atomic number 16 – 8 = 8 neutrons How many electrons? Same as atomic number if there are no superscript by letter If there is a superscript… always do the opposite operation to the atomic number. If it says 2-, then you ADD 2 If it says 3+, then you SUBTRACT 3 It says 2- here, so you add 2 to the atomic number (8 + 2 = 10 electrons) 8 O 2- 16

6 6 12 14 Changing the Neutrons Has 6 neutrons Has 8 neutrons ISOTOPES = atoms that are the same element (they have the same number of protons) but they have a different number of neutrons 6 6 Atomic Number C Atomic Number C 12 14 Mass Number Mass Number 12 - 6 protons = 6 neutrons Has 6 neutrons 14 - 6 protons = 8 neutrons Has 8 neutrons

Important Terms to Know Element Substance that cannot be broken down into a smaller substance by chemical means; all atoms have the same number or protons; H or O or Fe or Au Molecule 2 or more atoms bonded together; H20 or C6H12O6 Ion A positively or negatively charged atom; the atom has lost or gained an electron Atomic Number = Z Number of protons in the nucleus Mass Number = A Number of protons + neutrons in the nucleus of an atom Charge of ion (Number of protons) – (number of electrons) Valence electrons Electron in the outermost shell of the atom; important in bonding

O 8 16 Neutral Atom vs. Ion Neutral Atom (Example: Oxygen Atom) 6 electrons (6-) Neutral Atom (Example: Oxygen Atom) Has specific number of protons Oxygen Atom = __8 protons__(ALWAYS) Number of neutrons is similar to protons Oxygen Atom = __8 neutrons___ Number of electrons is the same as protons Oxygen Atom = __8 electrons___ Ion (Example: Oxygen Ion) Oxygen Ion = _8 protons___(ALWAYS) Oxygen Ion = __8 neutrons__ Number of electrons is DIFFERENT from protons Oxygen Ion = __10 electrons__ 2 electrons (2-) 8protons (8+) 8neutrons (0) 8 O 16 8 electrons (8-) 2 electrons (2-) 8protons (8+) 8neutrons (0)

16 8 16 2- 8 Atomic Number (Z) 8 protons = 8 Mass Number (A) 8 protons + 8 neutrons = 16 amu Charge (8+ protons) + (8- electrons) = 0 8 protons – 8 electrons = 0 O 2 e (2-) 8 8 P (8+) 8 N (0) Neutral Atom 16 8 e (8-) Atomic Number (Z) 8 protons = 8 Mass Number (A) 8 protons + 8 neutrons = 16 amu Charge (8+ protons) + (10- electrons) = 2- 8 protons – 10 electrons = 2- O 2 e (2-) 2- 8 8 P (8+) 8 N (0) Ion

An atom has a mass number (A) of 35. Practice Problem #1 An atom has a mass number (A) of 35. If it has 17 protons, how many neutrons does it have? 35 – 17 = 18 neutrons What is the atomic number (Z)? 17 What element would it be? Chlorine If it has 17 electrons, what would the charge on the atom be? 17 protons – 17 electrons = 0 (it is a neutral atom)

An atom has a mass number (A) of 24. Practice Problem #2 An atom has a mass number (A) of 24. If it has 12 protons, how many neutrons does it have? 24 – 12 = 12 neutrons What is the atomic number (Z)? 12 What element would it be? Magnesium If it has 10 electrons, what would the charge on the atom be? 12 protons – 10 electrons = 2+ (it is an ion)

An atom has a mass number (A) of 14. Practice Problem #3 An atom has a mass number (A) of 14. If it has 7 protons, how many neutrons does it have? 14 – 7 = 7 neutrons What is the atomic number (Z) 7 What element would it be? Nitrogen If it has 10 electrons, what would the charge on the atom be? 7 protons – 10 electrons = 3- (it is an ion)

Exit Ticket 1. Which statement about the atomic nucleus is correct? A. The nucleus is made of protons and neutrons and has a negative charge. B. The nucleus is made of protons and neutrons and has a positive charge. C. The nucleus is made of electrons and has a positive charge. D. The nucleus is made of electrons and has a negative charge.

2. The charge of an electron is -1 -2 +1

3. Atoms have no electric charge because they: have an equal number of charged and noncharged particles. B. have neutrons in their nuclei. C. have an equal number of electrons and protons. D. have an equal number of neutrons and protons.

An atom’s mass number equals the number of: protons plus the number of electrons. protons protons plus the number of neutrons. neutrons.