Chapter 4 “Atomic Structure”

Introduction to the Atom and Atomic Models

DEMOCRITUS 400 BC Ancient philosopher: Father of the Atom Democritus believed all things consisted of tiny indivisible units. He called these tiny units he called atomos. The Greek word for “can not be cut” or “indivisible”

John Dalton (1799)  Developed what is considered to be the 1 st Atomic Theory  Was born into a modest Quaker family in England  Began lecturing in public at the age of 12

Dalton’s Model (1799) Dalton's model was that the atoms were tiny, indivisible, indestructible particles and that each one had a certain mass, size, and chemical behavior that was determined by what kind of element they were. Dalton's model was that the atoms were tiny, indivisible, indestructible particles and that each one had a certain mass, size, and chemical behavior that was determined by what kind of element they were.

Dalton’s Model Dalton’s model of the atom was similar to a tiny billiard ball. Dalton’s model of the atom was solid and had no internal structure.

Dalton’s Atomic Theory elements consisted of tiny particles called atoms. elements consisted of tiny particles called atoms. all atoms of an element are identical all atoms of an element are identical atoms of each element are different from one another ; they have different masses. atoms of each element are different from one another ; they have different masses. compounds consisted of atoms of different elements combined together. compounds consisted of atoms of different elements combined together. chemical reactions involved the rearrangement of combinations of those atoms. chemical reactions involved the rearrangement of combinations of those atoms.

Flaws in Dalton’s Model Dalton’s falsely believed that the atom was the most fundamental particle. Dalton’s falsely believed that the atom was the most fundamental particle. We now know the atom is made up of even smaller particles we call the proton, neutron and electron. We now know the atom is made up of even smaller particles we call the proton, neutron and electron. Dalton’s theory could also not account for the formation of ions (charged particles) Dalton’s theory could also not account for the formation of ions (charged particles)

Daltons Atomic Model Summary Called: Billiard Ball Model Called: Billiard Ball Model Could account for Could account for Atoms of different atomic masses Atoms of different atomic masses Elements were tiny particles Elements were tiny particles Could NOT account for Could NOT account for Though atom was smallest particle Though atom was smallest particle Did not have an internal structure Did not have an internal structure The formation of charged particles The formation of charged particles

John J. Thomson (1897) Discovered the electron using the Cathod Ray Tube (CRT) Discovered the electron using the Cathod Ray Tube (CRT) Thomson found that the beam of charge in the CRT was attracted to the positive end of a magnet and repelled by the negative end. Thomson found that the beam of charge in the CRT was attracted to the positive end of a magnet and repelled by the negative end.

Thomson’s Hypothesis Concluded that the cathode beam was a stream of negative particles (electrons). Concluded that the cathode beam was a stream of negative particles (electrons). He tested several cathode materials and found that all of them produced the same result. He tested several cathode materials and found that all of them produced the same result. He also found that the charge to mass ratio was the same for all electrons regardless of the material used in the cathode or the gas in the tube. He also found that the charge to mass ratio was the same for all electrons regardless of the material used in the cathode or the gas in the tube. Thomson concluded that electrons must be part of all atoms. Thomson concluded that electrons must be part of all atoms.

Thomson’s atomic model Called the “plum-pudding” it was the most popular and most wildly accepted model of the time. Called the “plum-pudding” it was the most popular and most wildly accepted model of the time.

Thompsons atomic model could account for….. the atom having an internal structure the atom having an internal structure Light given off by atoms Light given off by atoms Atom with different atomic masses Atom with different atomic masses

Thompsons atomic model could NOT account for….. Empty space (had atom filled with positive pudding) Empty space (had atom filled with positive pudding) Formation of ions Formation of ions

Gold Foil Experiment Conducted by students of Rutherford. Conducted by students of Rutherford. Proved that all atoms had a tiny, positively charged center. Proved that all atoms had a tiny, positively charged center. Confirmed that atom’s were mostly empty space. Confirmed that atom’s were mostly empty space.

Rutherford ~ early 1900s α-particle interaction with matter studied in gold foil experiment α-particle interaction with matter studied in gold foil experiment

Rutherford's Nuclear Model 1. The atom contains a tiny dense center 1. The atom contains a tiny dense center the volume is about 1/10 trillionth the volume of the atom the volume is about 1/10 trillionth the volume of the atom 2. The nucleus is essentially the entire mass of the atom 2. The nucleus is essentially the entire mass of the atom 3. The nucleus is positively charged 3. The nucleus is positively charged the amount of positive charge of the nucleus balances the negative charge of the electrons the amount of positive charge of the nucleus balances the negative charge of the electrons 4. The electrons move around in the empty space of the atom surrounding the nucleus 4. The electrons move around in the empty space of the atom surrounding the nucleus

Rutherford’s atomic model (1911) Could account for: Could account for: Empty space Empty space Ions Ions Internal structure Internal structure Light given off when heated to high temperature. Light given off when heated to high temperature. Could not account for: Could not account for: Stability Stability

Philipp Lenard (1903) Aluminum foil experiment Aluminum foil experiment Lenard found that a beam of electrons was able to pass through a sheet of Al foil with almost no deflection. Lenard found that a beam of electrons was able to pass through a sheet of Al foil with almost no deflection. Lenard correctly concluded that the majority of an atom’s volume is empty space. Lenard correctly concluded that the majority of an atom’s volume is empty space.

Lenard’s atomic model Lenard’s model was composed of dynamids. Lenard’s model was composed of dynamids. Lenard calculated the size of a dynamid based on his experimental results and found it to be 1 billionth (1/1,000,000,000) the size of the atom. Lenard calculated the size of a dynamid based on his experimental results and found it to be 1 billionth (1/1,000,000,000) the size of the atom.

Lenard’s model could account for: Different atomic masses (based on the number of “dynamids”). Different atomic masses (based on the number of “dynamids”). The internal structure of an atom The internal structure of an atom The fact that most of the atom was empty space. The fact that most of the atom was empty space.

Flaws in Lenard’s model Formation of Ions (gaining or losing charge) Formation of Ions (gaining or losing charge) The light given off by materials when heated to a high temperature. The light given off by materials when heated to a high temperature.

First to present an atomic model close to the presently accepted model. He came up with his model in Hantaro Nagaoka

Nagoka’s Model Nagoka’s model of the atom was unstable. Nagoka’s model of the atom was unstable. According to the laws of planetary motion, the atom would collapse over time. According to the laws of planetary motion, the atom would collapse over time.

Planetary model Planetary model used to explain electrons moving around the tiny, but dense nucleus Planetary model used to explain electrons moving around the tiny, but dense nucleus Nucleus contains Nucleus contains Protons- existence proposed in 1900s Protons- existence proposed in 1900s Neutrons- existence proposed in 1930s Neutrons- existence proposed in 1930s

Successes of Nagoka’s model Atoms were able to give off electrons to form ions. Atoms were able to give off electrons to form ions. Accounted for the experimental fact that atom’s were mostly empty space Accounted for the experimental fact that atom’s were mostly empty space Explained different atomic weights. Explained different atomic weights. Explained the light given off when heated to high temperatures. Explained the light given off when heated to high temperatures.

Bohr Questioned ‘planetary model’ of atom Questioned ‘planetary model’ of atom Electrons located in specific levels from nucleus (discontinuous model) Electrons located in specific levels from nucleus (discontinuous model) Proposed electron cloud model based on evidence collected with H emission spectra Proposed electron cloud model based on evidence collected with H emission spectra

Bohr’s Atomic Model (1913) Bohr was a student of Rutherford. Bohr was a student of Rutherford. Improved Rutherford’s model by proposing electrons are found only in specific fixed orbits. Improved Rutherford’s model by proposing electrons are found only in specific fixed orbits. These orbits have fixed levels of energy These orbits have fixed levels of energy This explained how electrons could give off light (gain or lose energy) This explained how electrons could give off light (gain or lose energy)

BOHR MODEL Electrons are placed in energy levels surrounding the nucleus Electrons are placed in energy levels surrounding the nucleus Nucleus (p + & n 0 ) 2e - 8e -

Bohr’s Atomic Model Could account for Could account for Internal structure Internal structure Atoms of different masses Atoms of different masses Atom being mostly empty space Atom being mostly empty space Light given off Light given off Formation of positive ions Formation of positive ions Flaws Flaws Only really worked for Hydrogen Only really worked for Hydrogen

Chadwick (1932) Discovered the neutron by bombarding Be with beta radiation. Discovered the neutron by bombarding Be with beta radiation. Nuclear fission released a neutron. Nuclear fission released a neutron.chart

Review Describe each of the 6 different atomic models. Give the Describe each of the 6 different atomic models. Give the Scientist Name Scientist Name Name of model Name of model What they could account for What they could account for What they could not account for (flaws) What they could not account for (flaws)

Subatomic particle summary ParticleDiscovery byYearexperiment ProtonRutherford1911Gold Foil Experiment ElectronThompson1887The response of cathode ray tube to a magnetic and electric fields NeutronsChadwich1932Bombarded Be with beta radiation and a neutron was released

Subatomic Particles Electron Proton Neutron NameSymbolCharge Relative mass Actual mass (g) e-e- p+p+ n0n / x x

Subatomic Particles (cont.) All atoms of an element have the same # of protons All atoms of an element have the same # of protons protons identify an atom  atomic # protons identify an atom  atomic # Atoms are electrically neutral Atoms are electrically neutral #p = #e - #p = #e - Only neutrons and protons contribute to an atoms mass Only neutrons and protons contribute to an atoms mass #n + #p = atomic mass

ISOTOPES = atoms with the same number of protons but DIFFERENT numbers of neutrons Mass Number Atomic Number Element Symbol Ex. Na-23 or Sodium-23 or 23 Na or 23 Na C-14 or Carbon-14 or 14 C or 14 C B-10 or Boron-10 or 10 B or 10 B

Isotope Practice Element has a. 6 p+, 8 n and 6 e- b. 6 p+, 6 n and 6 e- c. 19 p+, 21 n and 10 e- d. __p+, __ n and __ e- e. __p+, __ n and __ e- Symbol a.. b.. c.. d. Cu-65 e. H-2

Ions Ion is an atom that has gained or lost one or more electrons and now has a charge Ion is an atom that has gained or lost one or more electrons and now has a charge Metals always lose electrons to form POSITIVE ions Metals always lose electrons to form POSITIVE ions Non-metals always gain electrons to form NEGATIVE ions Non-metals always gain electrons to form NEGATIVE ions The charge of the element is show on the right side of the symbol as a super script The charge of the element is show on the right side of the symbol as a super script Example: Na +1, Zn +1, S -2, N -3 Example: Na +1, Zn +1, S -2, N -3

Ions practice Element Ca +2 Br -1 Al +3 I -1 Number of electrons ?

D. Average Atomic Mass weighted average of all isotopes weighted average of all isotopes on the Periodic Table on the Periodic Table round to 2 decimal places round to 2 decimal places

D. Average Atomic Mass EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16 O, 0.04% 17 O, and 0.20% 18 O. EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16 O, 0.04% 17 O, and 0.20% 18 O.

D. Average Atomic Mass EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.