How Big is an Atom? Imagine that you could increase the size of an atom to make it as big as an orange. 

How Big is an Atom? At this new scale, the orange would be as big as the Earth. 

What is an atom? Smallest unit into which matter can be divided, while still maintaining its properties. An Element is composed of ONE type of atom.

The atomic Model of Matter John Dalton (1803-1807) J.J. Thomson (1897) Aim: The scientific study of the atom began with John Dalton in the early 1800’s and has been revised through the years. The atomic Model of Matter John Dalton (1803-1807) J.J. Thomson (1897) Ernest Rutherford (1910) Niels Bohr (1913) Wave-Mechanical Model

DOES NOT mention subatomic particles The Dalton Model 1803 1) Each element is composed of indivisible atoms. 2) In an element, all the atoms are identical; atoms of different elements have different properties, including mass. 3) In a chemical reaction, atoms are not created, destroyed, or changed into other types of atoms. 4) Compounds are formed when atoms of more than one element combine. 5) Dalton’s model = solid, indivisible, sphere. DOES NOT mention subatomic particles

Solid Sphere No Charged Particles

J.J. Thomson 1897 Examined cathode rays (electric charge that flows from the negative electrode, (cathode) to a positively charged electrode, (anode). These cathode rays were the paths of negatively charged particles he called electrons. Cathode Ray Tube - YouTube PLUM PUDDING model: Positively charged sphere with electrons embedded in it like raisins in plum pudding. He gave the atom some structure.

Plum Pudding Model

What happens when you bite into a peach?

The Rutherford Model 1911 Bombarded thin gold foil with the radioactive nuclei of Helium atoms (+ charged alpha particles) and observed how these particles were scattered by the foils. 1 in 20,000 particles bounced back or were deflected, the rest past through the gold sheets. Rutherford's Model of the Atom - YouTube Conclusion 1) Most of the atom is empty space with a dense (+) charged nucleus. 2) The atom has a dense (+) nucleus. 3) The electrons are present and orbit the space surrounding the nucleus.

Rutherford Experiment

Neils Bohr 1913 The Bohr Model – electrons travel in fixed circular pathways or ORBITALS around the nucleus, held in place by the proton(s) in the nucleus. Why we see Light 1) Electrons absorb energy and jump to higher orbitals. The electron gives off the excess energy as light and falls back down to lower energy levels. 2) Light given off by the atoms corresponds to certain frequencies or energies.

Shows the area with the greatest probability of finding an electron(s) Wave Mechanical Model Shows the area with the greatest probability of finding an electron(s)

Bohr Model vs. Wave Mechanical Model Bohr's model gives the electron orbit an exact travel path. Wave Mechanical The electron(s) make an orbital cloud of the most probable location around the nucleus. 18

Bright Line Spectra

+ + + + Structure of an Atom Energy Levels or Orbitals - Made up of the subatomic particles: Protons (positive) Neutrons (neutral) Electrons (negative) - + + - + + - - Energy Levels or Orbitals

+ The Atom’s “CENTER” - - - Protons and neutrons are grouped together to form the “center” or nucleus of an atom. + - - - Notice that the electrons are not apart of the nucleus. They are found in the electron cloud.

Subatomic Particle Weight Comparison Expressed in Atomic Mass Units (AMU) - - + 1839 electrons = 1 neutron 1836 electrons = 1 proton + How do you think the mass of a neutron compares to that of a proton? 1 neutron ≈ 1 proton

Atoms are Electrically Neutral + + + + - - - - = No Charge + - - - - + + + + 8 electrons 8 protons Number of Protons = Number of Electrons

Electron e- Outside the nucleus 1- 1/1840 Proton p nucleus 1+ 1 amu Sub-atomic Particle Symbol Location Electric Charge Mass Atomic mass unit (AMU) Electron e- Outside the nucleus 1- 1/1840 Proton p nucleus 1+ 1 amu Neutron n

Atomic Number

Neutrons 1) Neutrons add mass to an atom, but they do not change the atom’s identity as an element. 2) Neutrons are located inside the nucleus with the protons. # of neutrons + # of protons = MASS NUMBER Mass number – Atomic number = # of neutrons 3) All atoms on the periodic table are electrically neutral. Give the symbol, atomic number, # of protons, neutrons, and electrons, and atomic mass for Argon.

Isotopic Symbols

Isotope Notation – Concept Check Atomic Number = Atomic Mass = Protons = Electrons = Neutrons =

5 protons + 6 neutrons = a mass number of 11 amu The total number of protons and neutrons in the nucleus What is the mass number of this atom? - - 5 protons + 6 neutrons = a mass number of 11 amu  3 +  4 - + - + - What is the overall charge of this atom?

Bohr Model vs. Wave Mechanical Model Niels Bohr s Atomic Model - YouTube Niels Bohr based his atomic model on his observations using Hydrogen… Hydrogen has only 1 electron. 31

Bohr Diagrams Find your element on the periodic table. Determine the number of protons and neutrons in the atom. How can we do this? Atomic Number = Proton number. Mass Number – Atomic Number = Neutron # 32

Bohr Diagrams Draw a nucleus with the number of protons and neutrons. Carbon has two energy levels, or shells. (electron configuration) Draw the shells around the nucleus. C 33

Bohr Diagrams C Add the electrons. Carbon has 6 electrons. The first shell can only hold 2 electrons. The second shell will contain the other 4 electrons. C 34

Bohr Diagrams Build a Bohr Diagram Check your work. You should have 6 total electrons for Carbon. How many total electrons can fit in the third shell? C 8 35

Absorption and Release of Energy by an electron 1) When an electron absorbs a specific amount of energy (known as quanta or quantum of energy), the electron becomes excited and moves or “jumps” to a higher energy orbital. 2) When the electron “jumps” to a higher energy level or orbital it is said to be in the excited state. 3) When the electron releases this excess energy, it releases the energy as a photon of light and falls to the ground state. 4) The color light that is emitted or released is determined by how many orbitals and which orbitals the electron “falls” back.

Orbitals Atomic Emission Animation - YouTube

Neils Bohr 1913 Bohr - YouTube

Visible-line spectrum. Bohr Model vs. Wave Mechanical Model Quantum Mechanics: The Structure Of Atoms - YouTube Bohr Model When a Hydrogen e– was excited, the light emitted was found to be composed of regularly spaced lines. Each element has a Visible-line spectrum. Wave Mechanical An atomic orbital is the region of space around the nucleus where the probability of locating an e– with a given energy is greatest.

The bright-line spectra for three elements and a mixture of elements are shown below. Identify all the elements in the mixture. Explain, in terms of both electrons and energy, how the bright-line spectrum of an element is produced. State the total number of valence electrons in a cadmium atom in the ground state.

Ground State vs. Excited State 1) Ground State – all electrons are in the lowest possible energy levels (normal) ex. 2 – 7 2) Excited State – if given additional energy, electrons will “jump up” to higher energy levels, temporarily. Excited State ex. 2 – 5 – 2 Ground State ex. 2 – 7

Bright Line Emission Spectra How does this happen? “Excited electrons” at higher energy levels will eventually release the extra energy and “fall back down” to ground state conditions. 2. During the “fall back”, energy is released as Visible Light Energy.

Bright Line – Emission Spectra What evidence indicates that electrons move around the nucleus in definite pathways?

How would you compare different element’s spectral line patterns to an individual’s DNA?

Unknown DNA Sample Match

1) Each element has a specific electron configuration and a corresponding emission spectrum. 2) Emission (bright line) spectrum can be used to identify (“fingerprint”) each element.

Use your Sun block to block UVA and UVB rays!

Lewis Structures of Atoms 1) The chemical symbol for the atom is surrounded by a number of dots corresponding to the number of valence electrons. 2) Valence electron(s) – number of electrons in the atom’s outermost orbital. These are the electrons involved in chemical bonding between atoms. Kernel – Nucleus (protons and neutrons) and all non-valence electrons. Lewis and Bohr 51

C Lewis Structures In your notes, try these elements on your own: H P Ca Ar Cl Al C

Lewis Structures of atoms and ions Mg O Mg 2+ O 2-

Sodium (Na) – Yellow flame with Na salts like NaCl, NaBr Potassium (K) – Violet flame with KCl, KBr, etc.

Isotopes of an element account for the average atomic mass Isotopes- Atoms of the same element can have the same number of protons, BUT different numbers of neutrons. Atoms with a few too many neutrons, or not quite enough, can sometimes exist for a while, but they're unstable.

How can we calculate the Average Atomic Mass for an atom? Atomic mass or atomic weight - the average mass of atoms of an element, calculated using the relative abundance of naturally-occurring isotopes of an element. Remember The mass on the periodic table is the average of all the naturally occurring isotopes of that element. C = 12.011

238U with an abundance of 99.28% 235U has an abundance of 0.72%

Carbon’s Naturally Occurring Isotopes

Carbon Naturally Occurring Isotopes 98.89% of C atoms are 12C 1.108% of C atoms are 13C

Σ (mass of isotope × relative abundance) Average mass of C with 98.89% C-12 and 1.108% C-13 ***Remember to divide the percentages by 100 98.89%/100% = .9889 1.108%/100% = .01108 Mavg= [(.9889)(12) + (.01108)(13)] Mavg = [(11.8668) + (0.14404)] Mavg = 12.011 amu Chemistry: Average Atomic Mass

Ions Ions: neutral atoms that have either gained or lost electron(s). Number of protons and neutrons remains the same. Cation: atom loses 1 or more electrons to become a Positively charged ion. Anion: atom gains 1 or more electrons to become a Negatively charged ion.

Which has a larger atomic radius, the neutral atom or the ion? Explain.