Chemistry : electrons in atoms

Good ol' Al

1905: Einstein publishes 4 of his 5 famous papers, one on the photoelectric effect Proposed that EM radiation had both wavelike and particlelike properties - a beam of light could be seen as both a set of waves and a stream of tiny particles These tiny particles - "packets" of energy - were called photons (no mass, but carries a quantum of energy)

A little history

A few elements, such as gold and copper, have been known for thousands of years. Yet by 1700, only about 13 had been identified.

Lewis Electron Dot Diagrams

A way of showing & keeping track of valence e-. How to write them? Write the symbol - it represents the nucleus and inner (core) e- Draw one dot for each valence e-, up to 2 per side (8 maximum) Follow Hund's rule! They don't pair up until they have to.

ELECTRONEGATIVITY

An atom's tendency to attract electrons in a chemical bond (same pattern as ionization energy); also known as electron affinity The closer the nucleus is to the "surface" of the atom, the closer it is to the e- in the atom it is bonding with. This makes it easier to attract those e-. increases going left to right decreases going down a group Highest: Fluorine Lowest: Francium

Using the Periodic Table to Determine Electronic Arrangement

An electron configuration organizes an atom's electrons according to certain rules. This configuration identifies the energy in an atom. Electrons tend towards the lowest energy orbitals possible, meaning they are as close to the nucleus as possible. Atoms in which the electrons are in the lowest energy levels possible are called "ground state" atoms.

learn three ways to write electron configurations.

Arrow Method -Numerical/Long Configuration -Noble Gas/Kernel Configuration

Atomic Radius - Group Trends

As we go down a group, each atom's electrons occupy another energy level. Therefore, the atoms get bigger.

top of a group

Atoms are smallest at the top of a group (fewer e- shells) and largest at the bottom IE decreases as AR increases (as atoms become larger, outermost e- moves farther from the nucleus, so it becomes easier to remove), so elements at the bottom of a group lose e- faster than those at the top when reacting with the same substance EN also decreases as AR increases (as atoms become larger, the nucleus needs to attract e- from farther and farther away), so the elements at the bottom of a group are less able to attract e- and those at the top will react faster

Antoine Lavoisier

French nobleman prominent in chemistry and biology Inherited at age 5 French Enlightenment 1st version of the Law of Conservation of Matter (later used by Dalton), recognized and named hydrogen & oxygen, helped construct metric system Wrote the first modern chemistry textbook, compiled 1st extensive list of elements

The Bohr Model of the Atom

I pictured the electrons orbiting the nucleus much like planets orbiting the sun. However, electrons are found in specific circular paths around the nucleus, and can jump from one level to another. Energy level of an electron analogous to the rungs of a ladder The electron cannot exist between energy levels, just as you can't stand between rungs on a ladder

Transition metals (d-block)

Include many colored compounds due to proximity and overlap of s and d orbitals Chromium: chrome and various paint colors, color in emeralds and rubies, alloys (mixtures of metals) like stainless steel (Fe, Cr, Ni) Coinage metals copper (alloys with Sn for bronze, Zn for brass, Ag for sterling silver; green patina), silver and gold (alloys with Ni)

Nonmetals

Include some gases, some solids, one liquid at room temperature Generally high IE, high EN, poor conductors, little or no luster, brittle solids Some have multiple allotropes (one pure element, different arrangements of atoms) like carbon Halogens (VIIA) are highly reactive (found only as compounds), can be very useful and dangerous Noble gases (VIIIA) are relatively inert (nonreactive), used in cryogenic research, neon signs, protective atmospheres, lasers

Dmitri Mendeleev, Father of the Modern Periodic Table

Late 1860s, Russian New idea: arrange elements by both atomic mass AND reactivity Two-dimensional agreement Allowed him to predict existence and properties of undiscovered elements!

Following Lavoisier

Lavoisier's list (1790s) contained 23 elements (some not really elements, like light and "caloric") 1800s - Industrial Revolution! Electricity, used to break compounds into component elements By 1870 (less than 100 years after Lavoisier), 70 elements were known Volumes of new information Needed standardization and organization

Mendeleev

Left blanks for undiscovered elements When discovered, he had made good predictions But, there were problems: Co and Ni; Ar and K; Te and I Unknown to Mendeleev, Julius Lothar von Meyer was also working on a table; however, his only contained 28 elements, only categorized them by their valence electrons, and he did not predict unknown elements

Quanta are TINY

Let's emphasize this. t-i-n-y. Many scientists found this idea disturbing; they thought that energy could be added to matter continuously Consider a cup of water in the microwave Temperature increases "continuously" to us, but actually in infinitesimal increments as its molecules absorb quanta of energy

Changing the energy

Let's look at a hydrogen atom, with only one electron in the first energy level. Heat, electricity, or light can move the electron up to different energy levels. The electron is now said to be "excited" As electrons fall back to the ground state, they release energy as electromagnetic radiation They may fall down in specific steps Each step has a different energy

Light as a wave and a particle

Light has both wave and particle properties Continuous vs. discrete

Quantized Light

Planck proposed that all light (all EM radiation, in fact) was quantized Planck also demonstrated mathematically that the energy of a quantum is related to ν (frequency): Equantum = hν h = 6.626 x 10-34 J•s, AKA Planck's constant Matter can absorb, emit, or contain energy only in whole-number multiples of hν (1 hν, 2 hν, etc.)

Principal energy level

Principal energy level (given the principal quantum number, n) = the energy level of the electron: 1, 2, 3, etc. These correspond to rows on the periodic table A normal hydrogen atom has 1 principal energy level for its electron, whereas a sodium atom has 3

Quantum Numbers

Principal quantum number (energy level): n = 1, 2, 3, 4, 5, 6, or 7 Sublevels s, p, d, f (g, h, i) are names by azimuthal, or orbital quantum number (nodes in a sublevel): l = 0 through (n - 1) Magnetic quantum number (orbital orientation): ml = - l through l Electron spin quantum number (spin of electron): ms = +1/2 or -1/2

Brought to you by Einstein

Scientists preferred the wave model of light, even though they knew it couldn't explain some things like emission spectra Einstein played a major role in promoting the particle model by using it to explain the photoelectric effect in a famous paper, dated 1905

By Energy Level

Second Energy Level Has s and p orbitals available 2 in s, 6 in p 8 total electrons First Energy Level Has only s orbital only 2 electrons Third energy levelHas s, p, and d orbitals 2 in s, 6 in p, and 10 in d 18 total electrons Fourth energy level Has s, p, d, and f orbitals 2 in s, 6 in p, 10 in d, and 14 in f 32 total electrons Beyond the fourth energy level, not all the orbitals will fill up. The orbitals do not fill up in a neat order. The energy levels overlap Lowest energy fill first.

Numerical Electron Configuration (AKA Long Notation)

Similar to the arrow method, but instead of arrows, we use numerical exponents to show the number of electrons in the orbitals. Same rules apply, same order of orbitals. Write each sublevel name (1s, 2s, etc.) in order, followed by an exponent equal to the number of electrons present in the sublevel. All the exponents should add up to the total number of electrons in the atom.

Henry Moseley

Some elements clearly out of order (based on properties) Early 1900s, English physicist Discovered that each element has a unique number of protons Arranged the elements by atomic number Fixed problems in Mendeleev's table

periodic law

Thanks to Mendeleev and Moseley, we now have the Periodic Law: When elements are arranged in order of increasing atomic number, there is a periodic repetition of their properties. That is, you have an element with certain properties. Then, later in the Periodic Table, you have another one with similar properties. (NOT identical, but similar!)

families/groups

The elements in a vertical column are a FAMILY (or GROUP) Elements have the same # of valence electrons and therefore similar physical and chemical properties

Explanation of atomic spectra

The energy level from which the electron starts is called its ground state - the lowest energy level.

IONIZATION ENERGY

The energy needed to remove one electron (the outermost one) from an atom The farther an electron is from the nucleus, the easier it is for it to be removed. Therefore, IE decreases as you move down a group, and increases as you move left to right. It takes a lot of energy to remove an electron from Fluorine because its outer shell is almost full Hardly any energy required to remove an electron from Sodium because it has one electron in the outer shell

ultra violet , visible, infrared

The further they fall, more energy is released and the higher the frequency. This is a simplified explanation! The orbitals also have different energies inside energy levels All the electrons can move around.

period

The horizontal row on the periodic table is named a PERIOD. Elements have the same n (principal energy level)

Periodic trend: REACTIVITY

The reactivity of an atom is tied to the atomic radius, the ionization energy, and the electronegativity, as well as the number of valence e- it has. Metals are generally large, have low ionization energies, and low electronegativities, so it is easy for them to lose e-, but difficult for them to attract e-. Thus, they tend to lose e- in reactions. Since metals need to lose e-, those with fewer to lose will react fastest; metals with lower ionization energies will also react fastest Metals are more reactive in the lower left corner, less reactive in the upper right.Nonmetals are generally smaller atoms with high IEs and high ENs - thus, it is easy for them to attract e-, but not to lose e-. Therefore, nonmetals tend to gain e- in reactions. Since nonmetals need to gain e-, those with fewer to gain will react fastest; nonmetals with higher electronegativities will also react fastest Nonmetals are more reactive in the upper right corner, less reactive in the lower left

Sublevels by Block

The sublevels in an energy level correspond to "blocks" on the periodic table

What does this have to do with quanta?

The wave model says that with enough time and exposure, even the lowest-energy and frequency light would be able to cause this effect. Not so! Every metal has a certain frequency below which no e- are ejected. So there must be a certain minimum amount of energy that must be absorbed by e- in order for them to escape.

Nature of Electromagnetic Waves

They are transverse (up and down, as opposed to longitudinal waves) waves without a medium (they can travel through empty space.). They travel as vibrations in electrical and magnetic fields. Have some magnetic and some electrical properties to them. Water and sound waves transfer energy from one place to another- they require a medium through which to travel. They are mechanical waves.

The Quantum Mechanical Model

Things that are very small behave differently from things big enough to see. The quantum mechanical model is a mathematical solution It is not like anything you can see.

Major areas of the periodic table

Three of the major classes of elements are: 1) metals, 2) nonmetals, and 3) metalloids

metalloids

border the stair-steps and have properties that are intermediate between metals and nonmetals.

Parts of a wave

crest, wavelength, origin, amplitude, trough

metals

electrical conductors, have luster, ductile, malleable, solid at room temp (except for Hg)

Aufbau principle

electrons enter the lowest energy orbitals available. Aufbau = "building up" or "construction" Formulated by Niels Bohr and Wolfgang Pauli This causes difficulties because of the overlap of orbitals of different energies - follow the diagram!

1st group of the periodic table

elements need to give up one e- to become stable. Based on the trends in atomic radius and ionization energy, can you explain why these elements increase in reactivity as you move down the group?

nonmetals

generally brittle and nonlustrous, poor conductors of heat and electricity, neither malleable nor ductile Some nonmetals are gases (O, N, Cl); some are brittle solids (S); one is a fuming dark red liquid (Br). Some are colored, some are colorless.

Ions Cations

positively charged ions remember cations = + (positive) Would a cation have a larger or smaller atomic radius than an uncharged atom?

electromagnetic spectrum

radiowaves Microwaves infrared visible light ultraviolet x rays gamma rays

Pauli Exclusion Principle

the  2 electrons in each orbital must  have opposite spins: one spin up  and one spin down. Wolfgang Ernst Pauli - Austrian pioneer of quantum physics, close friend of Niels Bohr and Werner Heisenberg A "spin up" electron is represented by an up arrow and a "spin down" electron is represented by a down arrow.

Hund's Rule

when filling a sublevel put one electron in each orbital (all with the same spin), then pair up  until finished Friedrich Hermann Hund - German physicist who worked with Schroedinger, Heisenberg, etc. Electrons want to be far apart from each other, in different orbitals. But since energy levels need to be filled from the bottom up, they are filled by first putting one electron in each orbital of a sublevel (all with the same spin), then pairing if necessary

Noble Gas Electron Configuration(AKA kernel or core notation)

(This is the shortest method) You must indicate the last noble gas element and then finish the configuration. Calcium is: [Ar] 4s2 Useful because it separates out the valence electrons (electrons in the outermost shell)

Atomic radius increases in these directions

(up) to the left to the left going down

Ionization energy and electronegativity increase in these directions

(up) to the right (up/ on the left side

John Newlands

1860s English-Italian analytical chemist Once masses were standardized, Newlands realized that periodic trends emerged when elements were arranged by atomic mass "Law of octaves" Didn't work for all known elements, but still a revolutionary idea

Planck's quantum theory

1900: German physicist Max Planck studied light emitted by heated objects 1918: Won Nobel Prize in physics, founded quantum physics A quantum of energy is the amount of energy required to move an electron from one energy level to another; also the smallest amount of energy an atom can gain or lose

Active Metals

All configurations end in s1 or s2 (1 or 2 valence e-)

A few elemental liquids

Br2 and Hg Cs and Ga become liquid at just above room temp

Non-white light

By heating a gas with electricity we can get it to give off colors. Passing this light through a prism breaks it down into its component colors too

The EMS

Different frequencies of light are different colors of light. There is a wide variety of frequencies and wavelengths and the whole range is called a spectrum

Atomic Spectrum

Each element gives off its own characteristic colors. They are unique, like fingerprints. Very useful for identifying elements. This is how we know what stars are made of.

Also, n = # of sublevels

Each energy level has as many sublevels (s, p, d, f, g, h, i) as its principal quantum number 1st principal energy level has 1 sublevel (s) 2nd principal energy level has 2 sublevels (s and p) 3rd principal energy level has 3 sublevels (s, p, and d)

Orbitals within sublevels

Each sublevel is divided into orbitals, whose shapes are described by Schrodinger's equation Orbital: a region of space in which there is over 90% probability of finding an e- One orbital can hold 2 electrons Different number of orbitals per sublevel, depending on orientation and shape Because of the way they are shaped, sublevels have different energies from each other; all orbitals within a sublevel have equal energy

Extension of Planck's work

Einstein calculated that: Ephoton = hν The energy of a photon must have a certain minimum value to cause the ejection of an e- Same equation as Planck's! Even small numbers of photons, given the right amount of energy, can cause the photoelectric effect - problem solved! Particle model gains ground

Quantum Mechanical Model

Energy is quantized - it comes in chunks. Since the energy of an electron is never "in between" there must be a quantum leap in energy. In 1926, Erwin Schrodinger derived a probability equation describing the possible energies and positions of electrons in an atom

Schrodinger's Wave Equation

Erwin Schrodinger Equation for the probability of a single electron being found along a single axis (x-axis

Sum it up

Every atom has a certain number of principal energy levels in which its electrons can be found (rows on the periodic table) Each level has as many sublevels as itself (4 blocks on the PT) Each sublevel contains a certain number of orbitals (depends on orientation and shape) Because of the way they are shaped, some sublevels are higher energy than others, but all orbitals within a sublevel have equal energy Each orbital can contain 2 electrons

ernest rutherford's model

Found dense positive structure at the center of the atom ("nucleus") Electrons surround and move around it; an atom is mostly empty space Did not explain how electrons occupied space, why they didn't fall into the nucleus, or the chemical properties of the elements Fundamentally incomplete - a better description of electron behavior was needed

Atomic Radius- Period Trends

Going from left to right across a period, electrons are added to the same energy level, but there is more nuclear charge because protons are also added. Electrons are pulled closer, so the atoms get smaller.

Seven elements occur in pairs of atoms (diatomic) in their elemental state

H2 N2 O2 F2 Cl2 Br2 I2

Eleven elemental gases

H2, He, N2, O2, F2, Ne, Cl2, Ar, Kr, Xe, Rn

Exceptions to the rule

Lowest energy to higher energy. Adding electrons can change the energy of the orbital. Full sublevels are the lowest energy, and the absolute best situation. However, half filled sublevels also have a low energy, and are next best Makes them more stable. Can change the filling order

PERIODIC TRENDS

Many properties of the elements change in a predictable way as you move through the periodic table Atomic radius Ionization energy Electronegativity Reactivity

Example: Nitrogen

Nitrogen has 5 valence electrons to show. First we write the symbol. Then add 1 e- at a time to each side until all five have been placed, pairing the fifth one.

Other Examples of Periodic Trends

Similarities in reactivity (in groups) Noble gases don't react! (Not with much, anyway) O reacts with H to make H2O, S reacts with H to make H2S, Se reacts with H to make H2Se, and so on!

The Photoelectric Effect

Take a metal and shine light on it. Electrons are emitted! Used to power photoelectric cells in things like solar-powered calculators

ATOMIC RADIUS

The distance from the center of an atom's nucleus to its outermost electron Atoms get larger going down a group Atoms get smaller moving left to right Largest: Fr Smallest: He

Light: electromagnetic radiation

The study of light led to the development of the quantum mechanical model. Light is a kind of electromagnetic radiation. Electromagnetic radiation includes many types: radio waves, micro waves, infrared, visible light, ultraviolet, X-rays, gamma rays Speed of light = c = 2.998 x 108 m/s All electromagnetic radiation travels at this rate when measured in a vacuum Also, c = λν (wavelength (m) times frequency (Hz))

Types of Electrons

Valence electrons - The s and p e- in the outermost (occupied) energy level responsible for chemical properties of atoms Core e- are in the energy levels below. Elements in the same column have the same outer e- configuration, and thus the same valence e-. Therefore, the number of valence e- are easily determined: same as the group number (A) of the element

White Light

White light is made up of all the colors of the visible spectrum. Passing it through a prism separates it.

Niels Bohr's Model

Why don't the electrons fall into the nucleus? Move like planets around the sun. In specific circular paths, or orbits, at different levels. A fixed amount of energy separates one level from another.

active metals alkali metals(IA)

are EXTREMELY reactive to air and water - found in nature only as compounds and must be stored under oil

active metals Alkaline earth metals (IIA)

are higher in density and melting point but less reactive, so more useful in making automotive parts more reactive as you go down the group (AM movie) (AEM movie)

MOST elements

are solid are metallic are groups of single atoms (monatomic) in their elemental state

Electron Configurations

are the way electrons are arranged in various orbitals around the nuclei of atoms.

7th group in the periodic table

elements need to acquire one extra e- to become stable. Based on the trends in atomic radius and electronegativity, explain why these elements DEcrease in reactivity as you move down the group.

Anions Ions

negatively charged ions remember aNions are Negative Would an anion have a larger or smaller atomic radius than an uncharged atom?