The Atom Atomic Models

Think with me…about sugar crystals, you can see that they are small crystals and every crystal is identical.Think with me…about sugar crystals, you can see that they are small crystals and every crystal is identical. –You may grind these particles into a very fine powder, but each tiny piece is still sugar. If you dissolve the sugar in water, the sugar particles become virtually invisible.If you dissolve the sugar in water, the sugar particles become virtually invisible. From Philosophy to Science

–You could even look at the sugar solution under a microscope and you’d still not be able to see the sugar. However, you know it is still there because you can taste it.However, you know it is still there because you can taste it. These kind of observations and logic patterns led ancient philosophers to ponder the design of the universeThese kind of observations and logic patterns led ancient philosophers to ponder the design of the universe From Philosophy to Science

There were two schools of thought of the composition of the cosmos…There were two schools of thought of the composition of the cosmos… –is everything in the universe continuous and infinitely divisible –Or, is there a limit to how small you can get? Particle theory was not the most popular early opinion, but was supported as early as Democritus in ancient Greece.Particle theory was not the most popular early opinion, but was supported as early as Democritus in ancient Greece. From Philosophy to Science

Democritus proposed that all the matter is composed of tiny particles called “Atomos”Democritus proposed that all the matter is composed of tiny particles called “Atomos” –These “particles” were thought to be indivisible Aristotle did not accept Democritus’ atom, he was of the “matter is continuous” philosophyAristotle did not accept Democritus’ atom, he was of the “matter is continuous” philosophy –Because of Aristotle’s popularity his theory was adopted as the standard From Philosophy to Science

By the 1700’s nearly all chemists had accepted the modern definition of an element as a particle that is indivisibleBy the 1700’s nearly all chemists had accepted the modern definition of an element as a particle that is indivisible It was also understood at that time that elements combine to form compounds that are different in their properties than the elements that composed themIt was also understood at that time that elements combine to form compounds that are different in their properties than the elements that composed them –However, these understandings were based on observations not empirical evidence From Philosophy to Science

There was controversy as to whether elements always combine in the same proportion when forming a particular compound.There was controversy as to whether elements always combine in the same proportion when forming a particular compound. –In the 1790’s, chemistry was revolutionized by a new emphasis on quantitative analysis because of new and improved balances This new technology led to the discovery of some new scientific understandingsThis new technology led to the discovery of some new scientific understandings From Philosophy to Science

The Law of Conservation of Mass:The Law of Conservation of Mass: –Proposed by Antoine Lavoisier –States that mass is neither created nor destroyed during ordinary chemical rxns or physical changes. –Which means the total mass of the reactants must equal the total mass of the products. From Philosophy to Science

++ Carbon, C Oxygen, O Carbon Monoxide, CO Mass x Mass y Mass x + Mass y  ++ Carbon, C Oxygen, O Mass x Mass y Carbon Monoxide, CO Mass x + Mass y

The Law of Definite Proportions:The Law of Definite Proportions: –The fact that a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the source of the compound NaCl is NaCl no matter if it is table salt (small crystals) or rock salt (large crystals)NaCl is NaCl no matter if it is table salt (small crystals) or rock salt (large crystals) From Philosophy to Science

Copper Carbonate

The Law of Multiple Proportions:The Law of Multiple Proportions: –If 2 or more different compounds are composed of the same 2 elements, then the ratio of the masses of the 2nd element combined with a certain mass of the 1st element is always a ratio of small whole numbers From Philosophy to Science

++ == CarbonOxygen Carbon Monoxide, 1:1 == Carbon Dioxide, 1:2 ++ CarbonOxygen 11 12

In 1808, John Dalton proposed an explanation for each of the proposed lawsIn 1808, John Dalton proposed an explanation for each of the proposed laws –He reasoned that elements were composed of atoms & that only whole #’s of atoms can combine to form compounds –His ideas are now called the Atomic Theory of Matter Atomic Theory

1.All matter is composed of extremely small particles called atoms 2.Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, & other properties ELEMENT 2 ELEMENT 2 ELEMENT 3 ELEMENT 3 ELEMENT 1 ELEMENT 1 ELEMENT 4 ELEMENT 4 Atomic Theory

3.Atoms cannot be subdivided, created, or destroyed 4.atoms of different elements combine in simple whole # ratios to form chem compds 5.in chemical rxns, atoms are combined, separated, or rearranged Atomic Theory

Through these statements, evidence could be gathered to confirm or discount its claimsThrough these statements, evidence could be gathered to confirm or discount its claims –Not all of Dalton’s claims held up to the scrutiny of experimentation –Atoms CAN be divided into even smaller particles –Not every atom of an element has an identical mass Atomic Theory

Dalton’s Atomic Theory of Matter has been modified.Dalton’s Atomic Theory of Matter has been modified. What remains is…What remains is… 1.All matter is composed of atoms 2.Atoms of any one element differ in properties from atoms of another element One of the disputed statements of Dalton was that atoms are indivisibleOne of the disputed statements of Dalton was that atoms are indivisible Atomic Theory

–In the 1800’s it was determined that atoms are actually composed of several basic types of smaller particles –it’s the number and arrangement of these particles that determine the atom’s chemical properties. The def. of an atom that emerged was, the smallest particle of an element that retains the chemical properties of that original element.The def. of an atom that emerged was, the smallest particle of an element that retains the chemical properties of that original element. Atomic Theory

All atoms consist of 2 regions that contain the subatomic particlesAll atoms consist of 2 regions that contain the subatomic particles –The nucleus –The electron cloud around the nucleus The nucleus is a very small region located near the center of the atomThe nucleus is a very small region located near the center of the atom –In every atom the nucleus contains at least 1 proton, which is positively charged particle and usually contains 1 or more neutral particles called neutrons Atomic Structure

The electron cloud is the region that surrounds the nucleusThe electron cloud is the region that surrounds the nucleus –This region contains 1 or more elec- trons, which are negatively charged subatomic particles –The volume of the electron cloud is much larger than the nucleus Atomic Structure

The discovery of the first subatomic particle took place in the late 1800’s.The discovery of the first subatomic particle took place in the late 1800’s. –A power source was attached to two metal ends of an evacuated glass tube, called a cathode ray tube. –A beam of “light” appears between the two electrodes called a cathode ray. Discovery of the Electron

Cathode Ray Electric Current

Steering Coils The electron beam is painting all 525 lines 30 times per sec, it paints a total of 15,750 lines per sec.

Investigators began to study the ray and they observed that…Investigators began to study the ray and they observed that… 1.An object placed in the path of the ray cast a shadow on the glass 2.A paddle wheel placed the path of the cathode ray began to spin 3.Cathode rays were deflected by a magnetic field 4.The rays were deflected away from a negatively charged object Discovery of the Electron

The first 2 observations support the idea that the ray is composed of tiny individual particles traveling through the vacuum tubeThe first 2 observations support the idea that the ray is composed of tiny individual particles traveling through the vacuum tube The second set of observations support the evidence that the ray is composed of a substance that is negatively charged.The second set of observations support the evidence that the ray is composed of a substance that is negatively charged.

Discovery of the Electron J.J. Thomson studied the rays and proved that they were tiny negative particles being emitted from the metal atoms.J.J. Thomson studied the rays and proved that they were tiny negative particles being emitted from the metal atoms. –Dubbed these tiny particles “electrons” Robert Millikan then used an ingenious investigation to calculate the mass to charge ratio of an atomRobert Millikan then used an ingenious investigation to calculate the mass to charge ratio of an atom –He determined that the electrons were not part of the mass of the atom.

First Atomic Model What can their work help us conclude about the atom?What can their work help us conclude about the atom? –atoms are composed of smaller particles, and one of these compo- nents is negatively charged –atoms are neutral, so there must be an opposing (+) charge –because E’s are essentially mass-less, an opposing substance that makes up the mass of the atom

Negative particles embedded in a sphere of positive plasma-like matter. THINK… Chocolate Chip Cookie Negative particles embedded in a sphere of positive plasma-like matter. THINK… Chocolate Chip Cookie

Discovery of the Proton

Discovery of the Neutron In 1932, the English physicist James Chadwick discovered yet another subatomic particle.In 1932, the English physicist James Chadwick discovered yet another subatomic particle. –the neutron is electrically neutral –It’s mass is nearly equal to the proton Therefore the subatomic particles are the electron, proton, and neutron.Therefore the subatomic particles are the electron, proton, and neutron.

electron e-e-e-e x proton p+p+p+p x neutron n0n0n0n001 Structure of the Atom

Atomic Structure Scientists still didn’t really understand how the particles were put together in an atom.Scientists still didn’t really understand how the particles were put together in an atom. –This was a difficult question to resolve, given how tiny atoms are. Most thought it likely that the atom resembled Thomson’s modelMost thought it likely that the atom resembled Thomson’s model

Rutherford Model In 1911, Ernest Rutherford et al. provided a more detailed picture of the internal structure of the atomIn 1911, Ernest Rutherford et al. provided a more detailed picture of the internal structure of the atom In his experiment, Rutherford directed a narrow beam of alpha particles at a very thin sheet of gold foil.In his experiment, Rutherford directed a narrow beam of alpha particles at a very thin sheet of gold foil. –Alpha particles (  ) are He atoms that have been stripped of their electrons

Rutherford Model According to Thomson’s model, the heavy, positive alpha particles should pass easily through the gold, with only a slight deflectionAccording to Thomson’s model, the heavy, positive alpha particles should pass easily through the gold, with only a slight deflection –And mostly that’s how it happened. –However, they found 1 in every 8000 particles had actually been deflected back toward the source.

Rutherford Model Rutherford suggested a new structural model of the atom.Rutherford suggested a new structural model of the atom. –He stated that all the positive charge and the mass is concentrated in a small core in the center of the atom, AKA nucleus –And that the atom is mostly empty space with electrons surrounding the positively charged nucleus like planets around the sun.

Rutherford Model

Rutherford’s planet system model was an improvement over earlier models, but it was still not complete.Rutherford’s planet system model was an improvement over earlier models, but it was still not complete. –Physics says that electrons can’t orbit the nucleus without losing energy, Losing energy would cause the electron to spiral into the nucleus.Losing energy would cause the electron to spiral into the nucleus. The attraction of the electron to the nucleus would cause it to spiral into the nucleus as wellThe attraction of the electron to the nucleus would cause it to spiral into the nucleus as well

Bohr Model Niels Bohr proposed a new model that would allow the electrons to be outside the nucleus and in orbit around the nucleus.Niels Bohr proposed a new model that would allow the electrons to be outside the nucleus and in orbit around the nucleus. –His model coupled Rutherford’s model with a new concept of energy in Physics called quantum mechanics, Bohr proposed that the electrons aren’t on any random orbit around the nucleus, they are on “special” orbitsBohr proposed that the electrons aren’t on any random orbit around the nucleus, they are on “special” orbits

Bohr Model Bohr’s Model restricts the orbits on which an electron can beBohr’s Model restricts the orbits on which an electron can be –The bases for what orbit an electron is allowed is entirely based on how much energy the electron has If it has any more energy or any less energy it would be forced to be on a different path of different energyIf it has any more energy or any less energy it would be forced to be on a different path of different energy –The energy of the electron is quantized, which means it is of a very specific quantity

Bohr Model –Each path or level of energy that the electron is on is given a label of “n” Such that n=1 is the closest energy level to the nucleusSuch that n=1 is the closest energy level to the nucleus n=2 is higher in energy and outside of, but adjacent to n=1, and so on…n=2 is higher in energy and outside of, but adjacent to n=1, and so on… –Each energy level can only hold a certain number of electrons (2n 2 ) n=1 can hold 2 electronsn=1 can hold 2 electrons n=2 can only hold 8 electronsn=2 can only hold 8 electrons n=3 can hold 18 electronsn=3 can hold 18 electrons Etc.Etc.

Bohr Model Bohr Model of the Atom Model describes the paths of electrons as energy levels. The electrons are only allowed to have a certain amount of energy which restricts their path around the nucleus.

Atomic Structure With the exception of Hydrogen, every nucleus contains 2 kinds of particles protons and neutronsWith the exception of Hydrogen, every nucleus contains 2 kinds of particles protons and neutrons –they make up the mass of the atom (Mass Number = Protons + Neutrons) Proton has a charge equal to but opposite of the charge of an elec.Proton has a charge equal to but opposite of the charge of an elec. –Atoms are neutral because they contain equal #’s of protons & electrons

Structure of the Atom The atoms of different elements differ in the # of protons in their nuclei and therefore in their positive chargeThe atoms of different elements differ in the # of protons in their nuclei and therefore in their positive charge –The # of protons the atom contains determines the atom’s identity Only Oxygen contains 8 protonsOnly Oxygen contains 8 protons Only Fluorine contains 9 protonsOnly Fluorine contains 9 protons Only Neon contains 10 protonsOnly Neon contains 10 protons

Structure of the Atom The nucleus is composed of a densely packed cluster of protons, which are all electrically positiveThe nucleus is composed of a densely packed cluster of protons, which are all electrically positive –Don’t like charges repel? –Why don’t they fly apart? When 2 protons are in very close proximity, there is a strong force of attraction between them.When 2 protons are in very close proximity, there is a strong force of attraction between them. –similar attraction exists when neutrons are close

Structure of the Atom These short-range p + -n 0, p + -p +, & n 0 -n 0 forces hold the nuclear particles together, A.K.A strong nuclear forces.These short-range p + -n 0, p + -p +, & n 0 -n 0 forces hold the nuclear particles together, A.K.A strong nuclear forces. –When these nuclear forces are strong enough the atom is stable –If the forces are not strong enough the atom (heavier atoms) the atom is unstable and becomes radioactive.

Counting Atoms Basic Truth: All atoms contain the same basic parts, but atoms of different elements have different numbers of protons.Basic Truth: All atoms contain the same basic parts, but atoms of different elements have different numbers of protons. –The PT lists atoms in consecutive order by their Atomic Number (Z) –The atomic number is directly related to the number of protons in the nucleus of each atom of that element

Counting Atoms The atomic number is found above the elemental symbol on the PT and it defines the type of elementThe atomic number is found above the elemental symbol on the PT and it defines the type of element –Atomic #47 can only be Ag and it also can only have 47 protons in each nucleus –Because atoms are neutral, we know from the atomic number the atom must also contain 47 electrons.

Counting Atoms The total number of protons & neutrons determines the mass of the atomThe total number of protons & neutrons determines the mass of the atom –Called the Mass Number –A Carbon atom, has 6 protons and 6 neutrons, so its mass number is 12 If you know the atomic number & mass number of an atom of any element, you can determine the atom’s compositionIf you know the atomic number & mass number of an atom of any element, you can determine the atom’s composition

ATOMS OF THE 1 ST TEN ATOMS NAMESYMBOL ATOMIC # p+p+p+p+ n0n0n0n0 MASS # e-e-e-e- HydrogenH11011 HeliumHe22242 LithiumLi33473 BerylliumBe44594 BoronB CarbonC NitrogenN OxygenO FluorineF NeonNe

Counting Atoms Every Cl atom has 17 protons, w/o exception, but not every Cl atom has 18 neutrons.Every Cl atom has 17 protons, w/o exception, but not every Cl atom has 18 neutrons. –Atoms with the same # of protons but contain different #s of neutrons are called isotopes. Since isotopes of an element have different #s of neutrons they have different massesSince isotopes of an element have different #s of neutrons they have different masses

Counting Atoms Isotopes are chemically alike because they have identical numbers of protons and electronsIsotopes are chemically alike because they have identical numbers of protons and electrons –It’s the electrons and protons that are responsible for chemical behavior Isotopes can be noted using hyphen notation (Cl-35 vs Cl-37)Isotopes can be noted using hyphen notation (Cl-35 vs Cl-37) –elemental symbol hyphen mass number

Isotope: one of two or more atoms having the same number of protons but different numbers of neutrons or Na-23 or Na-24

Practice NameSymb Atomic # Mass # # p + # e - # n 0 Isotopic Symbol Strontium W 82 70