★The Atom★The Smallest Pieces of Matter★Value of Theories

★In order to unlock natureʼs secrets man has an orderly approach for this-scientific method ★In the scientific method you use a hypothesis or a possible explanation of a happening or a phenomena. ★A hypothesis can be tested by experimentation and if the findings are in agreement then a probable explanation or theory may be developed

★Theory to Law ★Continued and repeated experimentation which verifies the original explanation, or its modifications, may be eventually be recognized as a law or scientific statement of fact.★It is important that we are flexible enough to think beyond absolute. Too many times we develop ruts where we do not want to get out of, which then limits us.

★The Importance of the Imagination ★The imagination enables scientist to develop new hypothesis which enables them to find improvements in our lives and other advancements for mankind. ★Hypothesis, theories, and laws provide the ground work for further development in the field of chemistry and other science fields. More on the★Also models are important in science. They help us conceptualize concepts that may be challenging to us

★however- you must also keep in mind the limitations★Importance of Curiosity

★It was the wondering about the nature of matter, seeking to explain research data obtained from experimentation, that led to the formulation of the atomic, kinetic, and electronic theories which have been of such value in our understanding of matter.

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★History of the development★600 BC Thales of Miletus discovered that a piece of amber, after rubbing it with fur, attracts bits of hair and other light objects

★suggested that this mysterious force came from the amber★did not connect this force with any atomic particle

★460 BC Greek philosopher Democritus★Did a thought question★called the basic matter particles- atoms (means indivisible)

★Aristotle dismissed the atomic idea★Aristotle was considered more important

★1800 John Dalton (English)★ English Chemist★performed various experiments that showed that matter consisted of elementary particles★John Dalton conducted a series of experiments which included the analysis of a number of pure compounds and the study of gases ★He realized that these compounds had a definite composition by weight(a fact not entirely accepted in his day) ★As a result of this testing he developed a theory.

★Daltons Atomic Theory★1808 Dalton presented his theory in A New System of Chemical Philosophy★Dalton had no formal education★Had been experimenting since early childhood

★Postulates of the atomic theory★All matter consists of atoms, tiny indivisible particles of an element that cannot be created nor destroyed. (Derived from Democritus idea- reflects Lavosiers mass conservation)★2. Atoms of one element cannot be converted into atoms of another element. In chemical reactions, the atoms of the original substances recombine to form different substances.

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★3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element (unique mass and properties for the atoms of a given element)★4. Compounds result from the chemical combination of a specific ratio of atoms of different elements (law of definite composition)

★How the theory explains the mass law★Mass Conservations- Atoms cannot be created nor destroyed (postulate 1) or converted into other types of atoms (postulate 2). Therefore a chemical reaction in which atoms are combined differently cannot possibly result in mass change★Definite Composition- A compound is a combination of a specific ratio of different atoms (postulate 4), each of which has a particular mass (postulate 3). Thus each element in a compound constitutes a fixed fraction of the total mass★Multiple Proportions- Atoms of an element have the same mass (postulate 3) and are indivisible (postulate 1). The masses of element B that combine with a fixed mass of an element A give a small, whole number ratio because different numbers of B atoms combine with each A atom in different compounds

★Enabling us to? ★Dalton and Proust idea enables us to predict the amount of substances needed to make a desired compound★It is the beginning of chemistry

★Proves also ★Daltonʼs Theory also proves the law of conservation of mass which had previously been stated by Lavoisier. ★– Since the particles are indivisible and indestructible and that they unite in whole atoms, then matter is neither created not destroyed but conserved ★– However there is one exception, Nuclear reactions- some matter is converted into energy with a resulting loss of mass

★Daltonʼs Also... ★Dalton also realized that two elements could unite in different proportions by weight so as to form in more than one compound, observations which are summarized in his law of multiple proportions.

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★Updating Daltonʼs ★Daltonʼs theory has been proven true for certain parts, but not all. ★The atom is not truly indivisible.

★Definition of an atom ★An atom is the smallest particle of an element which can take part in chemical change (unite with other elements) ★Modern research has proven that atoms are complex structures made up of tiny electrical particles.

★Indivisible…. Not! ★An atom is indivisible by a nuclear change. ★It is not divisible under ordinary chemical reactions. ★Atoms of different elements can be regarded as chemical building blocks which make up chemical compounds.★It is electrically neutral, spherical entity composed of positively charged central nucleus surrounded by one or more negatively charged electrons★The electrons move rapidly with the available volume, held there by attraction of the nucleus★An Atomʼs diameter is about 20,000 times the diameter of the nucleus★The nucleus contributes to 99.7% of the atoms mass and occupies only one quadrillionth of its volume and it incredibly dense

Atomʼs Diameter

★Redefining ★An element is a substance which is made up of the same kind of atoms★It is the simplest type of matter with unique physical and chemical properties★It consists of only one kind of atom ★Compounds are substances consisting of two or more different kinds of atoms

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★consists of two or more different elements that are chemically bonded★elements in the compound are not just mixed together★their atoms have joined in a chemical reaction★Its properties are different from the parent elements

★Atomic Weights aka Atomic Mass★Atoms may be inconceivably small but they do have weight ★An atoms mass is 1.660 x 10 -24 grams ★That value is called the atomic mass unit (amu). ★Chemist use numbers to express these values.

★–Oxygen is 16.00 amu rather than 2.65 x 10 -23 grams★More on AMU

★Atomic weights are relative weights and require no units ★We could very well compare weights using grams, kilograms, grains, ounces, and pounds. ★You do not have to write amu after the weight. It is simply the weight.

★Not Droids ★Not all atoms of an element have the same weight or mass. ★Kinda like people ★Atoms of the same element that have different masses are called isotopes. ★So chemist average the weight on the periodic table

★Symbol Significance ★A chemical symbol represents more than the name of the element for which it stands

★– It stands for one atom of the element and weight of one atom ★O represents oxygen weighing 16 amu ★H represents hydrogen weighing 1 amu ★In most cases symbols do not stand for whole number atomic weights

★– Usually it is rounded off to the tenth position★Molecules

★Dalton referred to a union of two or more atoms as being compounds called complex atoms

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★As time marched on, it was discovered that many gaseous elements are made up of pairs of atoms instead of single atoms

★Count Amadeo Avogadro ★In 1811 Avogadro used the word molecule for all groups of atoms held in chemical combination ★However his research and his use of the word molecule did not come into effect until Stanislao Cannizzaro wrote about the idea of a molecule in his scientific writings.

★Advancement of Molecules ★Molecules vary in size. ★No matter how large the molecule is it can not be seen with a human eye ★A molecule contains at least two of the same or different kinds of atoms ★Molecules formed from the same element are called molecules of elements ★Molecules composed of different elements are called molecules of compounds ★In both cases they are diatomic (two atoms)

★Rare Gases ★Rare gases helium, neon, argon, krypton, xenon, and radon are monatomic molecules ★However most ordinary gases of a single element such as oxygen, hydrogen, nitrogen, and chlorine are diatomic

★Redefining ★Molecules are the smallest particle of a substance which has the properties of that substance. ★The properties of elements that usually exist in the solid state are not due to single atoms of that particular element but to clusters of atoms ★Copper as a group is a crystal ★It can only exist by themselves under high temperatures and then they do not have the same properties as the crystal

★Molecular Properties ★Most substances whether they are solids, liquids, or gases are composed of molecules.

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★Molecules come in different sizes. ★Molecules of different substances have different shapes and weights ★Some are simple and some are complex

★Molecular Properties Continued ★Whether a substance is brittle or elastic, hard or soft, transparent or opaque, or whatever properties it does have, because of its atoms and their arrangement.

★Keeping it together ★What keeps the molecules together? ★Van der Waals forces- electrical forces that bind the atoms together.

★– Solids and liquids experience it more than gases because gasses are so spread out. ★– At low temperatures, the molecules of a substance are sluggish and tend to group together in an orderly, more or less symmetrical patterns, often producing crystals. ★– The higher the temperature the faster the motion.

★Molecules and Formulas ★To write a molecule of a substance we simplify our life by writing a succession of symbols of each kind of atom it contains.

★NH3★Molecules and Formulas

★the succession of symbols is called a formula ★If there is more than one atom present in the compound, then the number is written as a subscript slightly below and to the right of the symbol ★If the molecule is monatomic (He, Na, C, etc) then the symbol represents a molecule of the substance

★More on that ★Diatomic molecules have the formula C 2, Cl2, H2, and so forth. ★Formulas of compounds are written to show the number and kind of the various elements, the subscript 1 never being used.

★Molecular vs. Empirical formulas

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★To know the actual formula of a substance it is necessary to know the elements present and the molecular weight

★– If this is known the formula represents the actual number, kind, and weight of the atoms present in each molecule is called the molecular formula

Example of Molecular and Empirical

★Empirical formula ★In some cases the formulas only represent the relative proportions of the individual elements and are called empirical formulas ★Some substances like starch have yet to be determined for their molecular weights.

★Significance of Formulas ★The symbol stands for an atom and its weight includes

★– 1. One molecule of an element or compound ★– 2. The constituents of the molecule ★– 3. The molecular weight, which is the sum of the weights of the constituents★Understanding formulas

★2 H ★2O--> what does it all mean?

★The 2 in front of the compound is called a coefficient. ★– So there are 4 hydrogens and 2 oxygens total ★– 1 is never written rather it is understood as a coefficient

★When combining- the number of atoms which will combine depends upon the valence electrons (outside shell)

★Kinetic Molecular Theory ★This theory explains the motion of molecules

★– Kinetic is Greek for motion

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★Molecules which make up matter are constantly moving ★The kinetic molecular theory of matter deals with the motion of molecules, particularly in gases, but also in liquids and solids. ★No matter the state the molecules are in constant motion

★Molecular motion in gases ★Gases consist of tiny separate molecules ★Molecules are relatively far apart and are in constant motion. The particles move in straight lines until they collide with other molecules and the walls of the container

★– This collision against the container is what causes pressure ★In the collisions the molecules rebound without loss of speed or energy and are therefore called elastic collisions.

★KMT and Gases ★The speed of the molecules determines their average kinetic energy or energy of motion

★– Also called heat energy (molecular motion) ★Increasing the temperature increases the speed of molecules and vice versa

★At a given temperature the KE of molecules of different gases will be the same, since heat energy is the same

★Kinetic Molecular theory★1. Particle volume- a gas consists of a large collection of individual particles with empty space between them. The volume of each particle is so small compared with the volume of the whole sample and it is assumed to be zero, each particle is essentially a point of mass★ 2. Particle Motion- the particles are in constant, random, straight line motion, except when they collide with the container walls or with each other★3. Particle Collisions- the collisions are elastic, which means that, like minute billiard balls, the colliding molecules exchange energy but do not lose any energy through friction. Thus their total kinetic energy is constant. Between collisions the molecules do not influence each other by attractive or repulsive forces

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★More Logic ★The heavier molecules move more slowly than the lighter molecules ★Due to the immense distances between the molecules, the weak forces of attraction between them, and their rapid motion, gases tend to have an indefinite volume and shape determined by their container only.

★Molecular motion in Liquids ★Brownian motion is random motion caused by the bombardment of molecules in a liquid ★Liquid molecules are closer to one another than gases and they also are held together more tightly than the gases by the van der Waals forces.

★Liquid movements ★If a liquid gains enough energy to escape then it evaporates ★The difference between evaporation and vaporization is that in vaporization heat is being added by an outside source

★More on Liquids ★When molecules jump from one state to another state the molecules build up pressure.

★– This pressure is called vapor pressure ★There is a constant loss gain from the surface of a liquid causes an equilibrium

★– Equilibrium- state of balance between two opposite reactions occurring at the same rates

★The total amount of reactants and products remain the same- there is physical equilibrium between the liquid and gas state.

★Molecular Motion in Solids ★Molecules are also in motion, but the motion is quite limited due to the van der Waals forces and other forces that causes the molecules to attract ★In general molecules of solids may be thought as vibrating about fixed points rather than sliding past each other as they apparently do in liquids

★The observations that led to the nuclear atom model★Dalton created a billiard ball model of the atom but did not predict the existence of subatomic charged particles, which were observed later in other experiments

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★It was however a start- Scientific Method, Continual adjustments, adjusting to new knowledge

★Discovery of the electron and its properties★for years we knew that matter and electric charge were related★The problem is in understanding where the charge came from★Cathode Rays

★evacuated glass tubes fitted with metal electrodes★When the electric power source was turned on, a ray could be seen striking the phosphor coated end of the tube and emitting a glowing spot of light★these rays were called cathode rays because they originated at the negative electrode (cathode) and moved to the positive electrode (anode)★The main conclusion was that the cathode rays consist of negatively charged particles found in all matter★The rays appear when these particles collide with the few remaining gas molecules in the evacuated tube.★These rays were later renamed electrons★Neon signs demonstrate this property★Aurora borealis also demonstrate this★Older computers and TVʼs used cathode rays to produce the image★Various test were conducted including testing with

★magnets- Ray bends in the magnetic field- Ray must contain charged particles★Electric Field- Ray bends toward positive plate- Consists of negative particles★Different rays produce identical results- all matter consists of these particles

★Mass and Charge of the electron★Mass/Charge ratio

★1897- British physicist JJ Thomson measured the ratio of the mass of the cathode ray particle to its charge

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★Thomson estimated that the cathode ray particle weighed less than 1/1000 as much as hydrogen (the lightest atom)★This was contradictory of Daltons Atomic Theory- it meant that there were smaller particles★We credit him with the naming of electrons

★Charge★In 1909 American physicist Robert Milikan measured the charge of the electron

★He did so by observing the movement of oil droplets in an apparatus that contained electrically charged plates and an xray source★Xrays knocked electrons from gas molecules in the air within the apparatus, and the electrons stuck to an oil droplet falling from a hole in a positively charged plate★with the electric field off, milikan measured the mass of the droplet from its rate of fall★then by adjusting the fieldʼs strength, he made the droplet hang suspended in the air, thus measured the total charge

Mass of electron

★The Structure of the Atom ★The Atom as Matter

★Daltonʼs atomic theory had problems ★It considered atoms to be hard, indivisible particles ★Did not explain why atoms reacted ★Also did not explain why atoms had varying abilities to combine with each other

★Need for a New Theory

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★Continued research on the nature of the atom after 1885 led to more understanding of the atomic structure

★Scientist of importance included ★Becquerel ★Thomson ★Rutherford ★Chadwick

★Parts of the Atom ★Three fundamental particles

★Protons ★Neutrons ★Electrons

★The number and arrangement of these three particles determines the nature and properties of the different kinds of atoms.

★Electron ★Discovered by J.J. Thomson in ★1897 ★Represented with a negative sign, or e, e- ★Has the mass of only 1/1837th that of the hydrogen atom ★Name is derived from Greek “elektron”- means amber- rub a piece of amber with fur or wool, it will attract light objects ★Cause of attraction is an electrical charge

★Protons ★Discovered by Ernest Rutherford in 1919 ★Represented with a + sign, the letter p, or p+ ★Charge is equal and opposite of an electron ★Mass is 1836/1837 that of an Hydrogen atom ★Gold Foil Experiment

★Neutrons ★Discovered by James Chadwick in 1932 ★Represented with the letter n, 0, n0

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★They have no charge, thus they are neutral has about the same mass as that of a proton

★Summation of the Parts ★Electron e, -, e- Negative, -1 0.00055 Surrounding the nucleus ★Proton p, +, p+ Positive, +1 1.00732 Inside the Nucleus ★Neutron n, 0, n0 Neutral, 0 1.00866 Inside the Nucleus

Name (symbol)

Relative Charge

Absolute Charge

(C)

Relative mass (AMU)

Absolute Mass (g)

Location in Atom

Discovered by and

experiment

Proton

Neutron

Electron

★The Electron Theory of Atomic Structure ★Understand that the knowledge and understanding of the \structure of the atom is not by direct observation but rather how the energy is absorbed or given off by large number of atoms

★Terminology ★Atoms are described by scientist in terms of particles and energy due to this phenomenon ★We will discuss this idea in more detail later Called Quantum Mechanics

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★Model ★One of the first major developments in this model is derived from Niels Bohr

★came up with the idea of a nucleus and shells of electrons ★Postulated that a strong electrical force kept the tiny universe intact

★The Atom ★Nucleus= where protons and neutrons are found at ★Positive charge ★most massive area ★Then a “Cloud” of electrons orbiting outside of the nucleus negative charge areas where electrons are relatively found at are called shells or energy levels ★Electrons spin on their axis

★Shells, Orbitals and Erwin Muller ★The Idea

★The idea was that there was a shell general region of electron movement around the nucleus ★Electrons generally stay in the region unless they are excited ★Each shell or region is a specific distance ★Orbitals are the paths that the electron goes within a shell ★Erwin Muller helped in this by photographing the location of atoms in metal crystals

★Electrons ★Electrons also spin while they revolve ★This spinning creates a magnetic field ★Electrons that spin opposite of one another are attracted to each other (Just like magnets) ★ Pauli exclusion principle (1925)- no more than 2 e- can occupy the same orbital (Due to Spin)

★Orderly Arrangement of Electrons ★Each atom has one or more shells depending upon the number of protons and electrons

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★Since orbitals are limiting, then there are only a certain number of electrons that can fit in one orbital

★Think ★Think about the periodic table and all that you have learned before ★What is the maximum capacity of this orbital?

★Based on Pauli Exclusion ★Principle, what is true about the spins?

★Think Activity ★Letʼs see if we can figure out some patterns.

★Energy Sublevels or Subshells ★Quantum Mechanics aka Quantum Theory

★Niels Bohr- 1913- developed the theory that electrons revolve at definite energy levels, and this is the basis of Quantum Theory ★In order for an electron to move it must gain or lose energy ★The amount of energy an electron must give off or take on is the difference between its original energy level and the one below it or above it

★How to See it ★We can see this change by using a spectroscope we see the light being emitted as the electron changes its orbital ★This is the foundations of quantum theory

★Transformation ★Overall this change of energy is a change from electrical energy or heat into light the color (energy) of the light depends upon the change or changes in energy levels made by the electrons ★The jumps from outer to inner energy levels are revealed by the characteristic lines observed for different elements in the spectroscope

★The s, p, d, f ★In orbitals you have subshells (energy sublevels) ★We designate these levels with letters like s,p,d,f ★Get out your Periodic Tables ★All electrons within a specific energy sublevel have the same amount of energy

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★s- Orbitals ★Smallest amount of energy the other orbitals will have increasing energies ★these levels have definite amounts or packets of energy also called quantum

★p, d, and f ★Letʼs take a look at the periodic table and lets see how this all fits

★Remember how I taught you to fold the periodic table- now we use it again

Reminder to what was previous- ITS FUNDAMENTAL FOR THIS COURSE★Atomic Structure

★The number of electrons in any atom equals the number of protons ★Atomic Number

★this determines the element!!!! ★Great way to classify elements into an orderly arrangement called the periodic table ground state is always neutral (protons equal electrons) ★sometimes symbolized as Z★it is the number of protons★All atoms of an element have the same atomic number, and the atomic number of each element is different from that of any other element★All carbon atoms (Z=6)- 6 Protons★All Oxygen atoms (Z=8)- 8 protons★Uranium atoms (Z= 92) - 92 protons★The first 92 elements are natural with 2 internal exceptions★After 92 those elements are non natural

★Mass Number (A)★the total number of protons and neutrons in the nucleus of an atom★Each proton and each neutron contributes to one unit in the mass number★Thus a carbon atom with 6 protons and 6 neutrons has a mass number of 12★Uranium atom has 92 protons and 146 neutrons in its nucleus and has the mass number of 238

★Atomic Symbol

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★element symbol★is based on it English, Latin, or Greek name★C for Carbon★S for Sulfur★Na for sodium (Latin for natrium)★To determine the number of neutrons simply subtract the mass number from the atomic number

Determination of Neutrons

★Structure of the Atom★the magnitudes of the charges possessed by a proton and an electron are equal, but the signs of the charges are opposite★ An atom is neutral because the number of protons in the nucleus equals the number of electrons surrounding the nucleus

★Chemical Activity ★Atoms with a full octet or filled outer shells do not combine with other atoms they are inert ★Noble gases ★Incomplete filled shells tend to combine with other kinds of atoms whose shells are also not filled ★do this by sharing, gaining, or losing electrons ★Chemical activity is determined by outermost electrons also called valence electrons

★Practice Shells ★Letʼs draw some atoms based on old ideas

★Three Rules of Filling ★Electrons always occupy orbitals of the lowest energy available

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★There can be a maximum of only two electrons in any given orbital. (spins will be opposite- Pauliʼs Exclusion principle) ★Electrons are added successively filling subshells with electrons in a specific order based on increasing energies of the subshells.

★New Eyes ★Filling orbitals and how to write electron configuration ★Letʼs Practice

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★Last Items ★What are Isotopes. We have been looking at the periodic table and the Atomic Mass Unit is not an even number. ★Why ★Those numbers are based on the abundancy of the isotopes.

★Isotopes ★Isotopes- an element that varies due to number of neutrons ★Remember that the element is determined by the number of protons. ★Isotopes have different weights and this difference can cause some elements to have different radioactivity ★note that the chemical properties remain virtually the same

★Calculations of Neutrons ★Take the difference between Atomic Mass and Atomic Number in order to determine the number of neutrons

★AN Isotope would be like ★C12 and C14

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★C14 is the isotope because C12 is the norm ★Antimatter

★1929 Dirac made a prediction that there must exist “extraordinary” electrons or particles that have the same mass but are opposite in charge. ★3 years later Anderson proved that there were positrons ★These particles make up antimatter and may be controlled by antigravity ★positron is the antiparticle of the electron★antiproton can form an antihydrogen atom★mixing matter and antimatter could lead to the annihilation of hoth and we believe that it will release high energy like photons (gamma rays) or other antiparticle-particle pairs★Dark matter versus antimatter- we have very strong experimental reasons to believe that they are not the same thing★If Dark matter and matter collided and if antimatter was dark matter, then there should be more explosions on a regular basis. Since this does not occur, we believe that antimatter and dark matter are different. ★More can be found at Antimatter:Mirror of the Universe

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