Chapter 9: Electrons in Atoms & the Periodic Table

Hund's Rule

electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible. When filling orbitals of equal energy, electrons fill them singly first, with parallel spins

Niels Bohr & Erwin Schrödinger

- (blank) & (blank), along with Albert Einstein, played a role in the development in quantum mechanics, yet they were bewildered by their own theory of wave-particle duality for the electron

Alkali metals

- (blank) Group 1 are among the most reactive metals since their outer electron configuration (ns^1) is 1 electron beyond a noble gas configuration a) if they can react to lose the electrons, they attain a noble gas configuration - this explains why the Group 1 metals tend to form 1+ cations

Alkaline Earth Metals

- (blank) Group 2 all have electrons configurations ns^2 & are therefore two electrons beyond a noble gas configuration a) in their reactions, they tend to lose two electrons forming 2+ ions & attaining a noble gas configuration

Halogens

- (blank) Group 7 all have ns^2np^5 electrons configurations & are therefore 1 electron short of a noble gas configuration a) in their reactions, (blank) tend to gain one electrons forming one minus ions & attaining a noble gas configuration

Periodic Properties: Ionization Energy

- (blank) increases as you move to the right across a period & decreases as you move down a column in the periodic table

infrared light

- (blank) light is next, with an even longer wavelength than visible light a) the heat you feel when you place your hand near a hot object is (blank) b) all warm objects, including human bodies, emit (blank) c) while (blank) is invisible to our eyes, (blank) sensors can detect it & are often used in night-vision technology to "see" in the dark d) in the (blank) region of the spectrum, warm-objects-- such as human bodies-- glow, much as a lightbulb glows in the visible region of the spectrum. warm areas appear as red & coolest area appear as dark blue

Hydrogen emission lines

- (look at picture= 2nd one) - since the amount of energy in a photon is directly related to its wavelength, the photon has specific wavelength - the light emitted by excited atoms consists of specific lines at specific wavelengths, each corresponding to a specific transition between two orbits EX: the line at 486 nm in the hydrogen emission spectrum corresponds to an electron relaxing from the n=4 orbit to the n=2 orbit - in the same way, the line at 657 nm (longer wavelength, & lower energy) corresponds to an electron relaxing from n=3 orbit to the n=2 orbit

Each element has its own atomic emission spectrum of light

- Ne atoms inside a glass tube absorb electrical energy & then remit the energy as red light - light emitted from a mercury lamp appears blue & light emitted from a hydrogen lamp appears pink

Chemistry & Health: radiation treatment for cancer

- X-rays & gamma rays are sometimes called ionizing radiation because the high energy in their photons can ionize atoms & molecules - when ionizing radiation interacts with biological molecules, it can permanently change one even destroy them - Doctors can use ionizing radiation to destroy molecules within unwanted cells such as cancer cells - in radiation therapy, doctors aim X-ray or gamma-ray beams at cancerous tumors - the ionizing radiation damages the molecules within the tumor's cells that carry genetic material, & the cell dies or stops dividing - healthy cells often inadvertently sustain damage during treatments, resulting in side effects such as fatigue, skin lesions & hair loss - doctors try to minimize the exposure of healthy cells by appropriate shielding & by targeting that tumor from multiple directions, minimizing the exposure of healthy cells while maximizing the exposure of cancerous cells

Light: Color in Objects

- a red shirt appears red because it reflects red light ; the shirt absorbs all the other colors of light except the red light. Our eyes see only the reflected light, making the shirt appear red

emission spectra of elements are not continuous

- a white light spectrum is continuous, with some radiation emitted at every wavelength. The emission spectrum of an individual element includes only specific wavelengths - look at the picture - the energy of each Bohr orbit, specified by a quantum number n= 1,2,3 is fixed or quantized - Bohr orbits are like steps of a ladder, each at a specific energy * It is impossible for an electron to exist between orbits in the Bohr model

Electron Configurations: how electrons occupy orbitals

- an electron configuration shows the occupation of orbitals by the electrons for a particular atom EX: Ground State hydrogen atom electron configuration H 1s^1---> number of electrons in orbital - the electron configuration tell us that hydrogen single is in the 1 s orbital

Electromagnetic spectrum (examples)

- arrange visible light, X-rays, & microwaves in order of increasing: a) wavelength: X-rays, visible light, microwaves b) frequency: microwaves, visible light, X-rays c) Energy per photon: microwaves, visible light, X-rays

Periodic Trends: atomic size has two factors

- as you move to the right across a period in the periodic table, atomic size decreases - the atomic size of an atom is determined by the distance between the outermost electron & the nucleus a) the size of an orbital depends on the principal quantum number - with each step across a period, the number of p+ in the nucleus increases a) this increase in the number of p+ results in a greater pull on the electrons from the nucleus, causing atomic size to decrease - as you move down a column in the periodic table, atomic size increases a)as you move down a column, the highest principal quantum number, n, increases -since the size of orbital increases with increasing principal quantum number, the electron that occupy the outermost orbitals are farther from the nucleus as you move down a column

UV light (Ultraviolet)

- between X-rays & visible light in the electromagnetic spectrum is (blank), familiar to us as the component of sunlight that produces a sunburn or suntan a) while not as energetic as gamma-ray or X-ray photons, (blank) photons still carry enough energy to damage biological molecules b) excessive exposure to (blank) increases the risk of skin cancer & cataracts & causes premature wrinkling of the skin

Microwaves

- beyond infrared light, at longer wavelengths still, are (blank), used for radar & in microwave ovens a) (blank) light has longer wavelengths & therefore lower energy per photon- than visible or infrared light b) (blank) light is efficiently absorbed by water & can heat substances that contain water I) substances that contain water, such as food, are warmed by the radiation of a microwave oven, but substances that do not contain water, such as plate, are not c) some types of dishes contain substances that absorb (blank) radiation, but most do not

Noble Gases

- calculations show that the atoms with eight valence electrons (or 2 for He) are predicted to the particularly low in energy & therefore stable a) (blank) are chemically stable, & thus relatively inert or nonreactive as accounted for by the quantum model - elements with electron configurations close to the (blank) are the most reactive because they can attain (blank) electron configurations by losing or gaining a small of electrons

Baseball paths & electrons probability maps

- contrast the behavior of a baseball with that of an electron - imagine a baseball thrown from the pitcher's mound to a catcher at home plate - the baseball's path can easily be traced as it travels from the pitcher to the catcher - in the quantum-mechanical world of the electron, the catcher could not exactly know where the electron would cross the plate for any given throw -he would have no way of putting his mitt in the right place to catch it - however, if the catcher kept track of 100s of electron throws, he could observe a reproducible statistical pattern of where the electron crosses the plate - he could even draw maps in the strike zone showing the probability of an electron crossing a certain area- AKA probability maps - to describe the behavior of a "pitched" electron, you would have to construct a probability map of where it would cross home plate

Summary of excited atoms

- electrons exist in quantized orbits at specific, fixed energies, & specific, fixed distances from the nucleus - when the energy is put into an atom, electrons are excited to higher-energy orbits - when an electron in an atoms relaxes (or falls) from a higher-energy orbit, the atom emits light - the energy ( and therefore the wavelength) of the emitted light corresponds to the energy of the emitted light is fixed & discrete

Energy ordering of orbitals for multi-electron atoms

- in multi-electron atoms, the sub shells within a principal shell do not have the same energy because electron to electron interactions a) different sub shells within the same principal shell have different energies - the 4 s sub shell is lower in energy that the 3 d sub shell, even though its principal quantum number is higher

Electron Spin

- in orbital diagrams, the direction of the arrow (pointing up or down) represents electron spin, a fundamental property of electrons - The Pauli exclusion principle states that orbitals may hold no more than 2 e- with opposing spins a) symbolize with two current arrows pointing in opposite directions

Principal quantum numbers of orbitals

- in the quantum-mechanical model, a number and a letter specify an orbital (or orbitals) - the lowest- energy orbital in the quantum mechanical model is called 1 s orbital a) it is specified by the # 1 & the letter S - the number is called the principal quantum number (n) & specifies the principal shell of the orbital

Electromagnetic Radiation (photons- particles of light)

- light can be viewed as a stream of particles a) a particle of light is called a photon i) we can think of a photon - the amount of energy carried in the packet depends on the wavelength of the light-- the shorter the wavelength, the greater the energy - light waves carry more energy if their crests are closer together (higher frequency & shorter wavelength) - violet light (shorter wavelength) carries more energy per photon than red light (longer wavelength)

Components of white light: ROY G BIV

- light is separated into its constituent colors- red, orange, orange, yellow, green, blue, indigo, & violet- when it is passed through a prism

Write electron configuration

- lower energy orbitals fill before higher-energy orbitals - orbitals can hold no more than 2 electrons each. when 2 electrons occupy the same orbital they must have opposing spins AKA Pauli exclusion principle - when orbitals of identical energy are available, all of these are 1st occupied singly by electron with parallel spins rather than electrons in pairs AKA Hund's rule

Periodic Properties: metallic character

- metals tend to lose electrons in their chemical reactions, while nonmetals tend to gain electrons - as you move across a period, ionization energy increase, which means that electrons are less likely to be lost in chemical reactions - (blank) decreases as you move to the right across a period & increases as you move down a column a periodic table

X-rays

- next on the electromagnetic spectrum, with longer wavelengths & lower energy than gamma rays are (blank), familiar to us from their medical use a) (blank) pass through many substances that block visible light & are used to image internal bones & organs b) like gamma- rays photons, (blank) photons carry enough energy to damage biological molecules c) while several yearly exposures to (blank) are relatively harmless, excessive exposure to (blank) increases cancer risk

Visible light

- next on the spectrum is (blank), ranging from violet (shorter wavelength, higher energy) to red (longer wavelength, lower energy) a) photons of (blank) do not damage biological molecules b) photons of (blank) cause molecules in our eyes to rearrange, which sends signals to our brains that result in vision

Representations of Orbitals

- orbitals are sometimes represented by dots, where the dot density is equal to the probability of finding the electron a) the dot density for the 1 s orbital is greatest near the nucleus & decreases farther away from the nucleus b) the electron is more likely to be found close to the nucleus than farther away from the nucleus - orbitals can be represented as geometric shapes that encompasses the volume within which the electron is found 90% of the time - if we superimpose the dot representation of the 1 s orbital on the shape representation we can see that most of the dots are withing the sphere when it is in the 1 s orbital - dot density & shape representations of the 1 s orbital: the dot density is proportional to the probability of finding the electron. The increase in dot density near the middle represents a high probability of finding the electron near the nucleus

The explanatory power of quantum mechanical model

- sodium tends to form Na+ ions, & fluorine tends to form F- ions - some elements are metals, & others are nonmetals - the noble gases are chemically inert, & the alkali metals are chemically reactive - the chemical properties of elements are largely determined by the number of valence electrons they contain a) their properties vary in a periodic fashion because the number of valence electrons is periodic

Quantum-Mechanical Model: atoms with orbitals

- the (blank) model of the atom replaced the Bohr model in the the early 20th century. In (blank) model, Bohr orbits are replaced with (blank) model orbitals - (blank) mechanics revolutionized physics & chemistry because, in the (blank) model, electrons do not behave like particles flying through space a) we cannot, in general, describe their exact paths - an orbital is a probability map that shows where the electron is likely to be found when the atom is probed; it does not represent the exact path that an electron takes as it travels through space

A pattern exists for the entire periodic table

- the 1st two columns on the left side of the periodic table are the s block - the six columns on the right side of the periodic table are the p block - the transition metals are the d block - the lanthanides & actinides (AKA inner transition metals) are the f block

electromagnetic spectrum

- the entire electromagnetic spectrum, with short-wavelength, high-frequency radiation on the right & long-wavelength, low-frequency radiation on the left. Visible light is the small sliver in the middle

The Bohr Model: atoms with orbits

- the great success of the (blank) of the atoms was that it predicted the lines of hydrogen emission spectrum - however, it failed to predict the emission spectra of other elements that contained more than one electron a) for this & other reasons, the (blank) was replaced with a more sophisticated model called the quantum-mechanical or wave-mechanical model

Energy increases with principal quantum number

- the higher the the principal quantum number, the higher the energy of the orbital - the possible principal quantum numbers are n= 1,2,3 with energy increases as n increases - since the 1 s orbitals has the lowest possible principal quantum number, it is the lowest energy shell, & has the lowest possible energy

Write the electron configuration for any element based on its position in the periodic table

- the inner electron configuration is the electron configuration of the noble gas that immediately precedes that element in the periodic table. Represent the inner configuration with the symbol for the noble gas in brackets - the outer electron can be determined from the element's position within a particular block (s, p, d, or f) in the periodic table. Trace the elements between the preceding noble gas & the element of interest & assign electrons to the appropriate orbitals -the biggest principal quantum number (highest n value) is equal to the row number of the element in the periodic table - for any element containing d electrons, the principal quantum number (n value) of the outermost d electrons is equal to the row number of the element minus one

Electrons Configurations: orbital diagrams

-another way to represent this information is with an orbital diagram, which gives similar information but shows the electron as an arrow in a box representing the orbital EX: Orbital diagram for ground-state hydrogen atom - look at the picture - the box is equal to the 1 s orbital, & the arrow within the box represents the electron in the 1 s orbital

Light: Electromagnetic Radiation

- the interaction of (blank) with atoms helped to shape scientists' models of the atom - (blank) is a form of electromagnetic radiation - (blank) is a type of energy that travels through space at a constant speed of 3.0 X 10^8 m/s (186,000 mi/s) - (blank) has properties of both waves & (blank) particles (wave-particle duality of light) - when the water surface is disturbed, waves have created that radiate outward from the site. The wave carries energy as it moves through the water - the wavelength of light λ (lambda) is defined as the distance between adjacent wave crests - Frequency: the frequency of light, v (nu, pronounced "noo"), is defined as the number of cycles or crests that pass through a stationary point in 1 second a) wavelength & frequency are inversely related- the shorter the wavelength the higher the frequency

Shapes of quantum-mechanical orbitals

- the letter indicates the sub shell of the orbital & specifies it shape a) the possible letters are s, p, d, & f, each with a different shape - orbitals within the s sub shell have a spherical shape

Radio waves

- the longest wavelengths of light are (blank), which are used to transmit signals used by AM & FM radio, cellular telephones, TV, & other forms of communication

Orbitals when n=3

- the next shell, n=3, contains 3 sub shells specified by s,p, & d a) the s & p sub shells contain the 3 s & 3 p orbitals, similar in shape to the 2 s & 2 p orbitals, but slightly larger & higher in energy - the d sub shell contains 5 d orbitals

Periodic trends in electron configurations of the main group elements

- the number of valence electrons for any main- group element is equal to the group number of its column. (He is an exception) - Cl has 7 valence electrons because it is in the column with group number 7A - the row number in the periodic table is equal to the number of the highest principal shell (n value) a) Cl is in row 3; it highest principal shell is the n=3 shell - remember that main-group elements are those in the two far left columns (1A, 2A), & the six far right columns (3A-8A) of the periodic table

From orbits to orbitals

- the quantum-mechanical model predicts the bright-line spectrum of hydrogen as well as the Bohr model does - the quantum-mechanical model can predict the bright-line spectra of other elements; the Bohr model cannot predict among spectra for atoms with more than 1 electron a) bohr model replaced with quantum-mechanical or wave-mechanical model - the Bohr model is still important because it provides a logical foundation to the quantum-mechanical model & reveals the historical development of scientific understanding

Gamma rays

- the shortest wavelength & most energetic photons are those of (blank) a) (blank) are produced by the sun, stars, & by certain unstable atomic nuclei on Earth b) excessive human exposure to gamma rays is dangerous because the high energy of (blank) photons can damage biological molecules

Ground states & excited states

- the single electron of an undisturbed hydrogen atom at room temp is in the 1 s orbital a) this is called (blank), or lowest energy state, of the hydrogen atom - the absorption of energy by a hydrogen atom can cause the electron to jump (or make a transition) from the 1 s orbital to a higher-energy orbital, the hydrogen atom is said to be in an excited state a) all the atoms of each element have one (blank) & many excited states

Periodic trends in electron configuration of the transition series elements

- the transition metals have electron configurations with trends that differ somewhat from the main-group elements - the principal quantum number of the d orbital being filled across each row in the transition series is equal to the row number 1 - for the 1st transition series, the outer configuration is 4s^2 3d^x (x= number of d electrons) a) two exceptions: Cr is 4d^1 3d^5 & Cu is 4s^1 3d^10 - these exceptions occur because a half-filled d sub shell & a completely filled d sub shell are particularly stable - the number of outer shell electron in a transition series does not change as you move across a period -the transition series represents the filling of core orbitals & the number of outer shell electrons is mostly constant; either 2 or 1 2 e- for 4s^2 3d^x 1 e- for 4s^1 3d^5 or 4s^1 3d^10

Electron configuration & the periodic table

- valence electrons are the electrons in the outermost principal shell (the principal shell with the highest principal quantum number, n) - electrons that are not in the outermost principal shell are called core electrons- more tightly bound EX: silicon has 4 valence electrons (those in the n=3 principal shell) & 10 core electrons - the elements within a column of the periodic table all have the same number of valence electron & similar outer electron configurations

Electrons in Atoms & the Periodic Table

- we examine two important models- the Bohr model & the quantum mechanical model- that propose explanations for the inertness of helium, the reactivity of hydrogen, & the periodic law a) these models explain how electrons exist in atoms & how those electrons affect that chemical & physical properties of elements

Excitation & Emission

- when a hydrogen atoms absorbs energy, an electron is excited to a higher- energy orbit. the electron then relaxes back to a lower-energy orbit, emitting a photon of light

Noble gas core notation

- when writing electron configurations for elements beyond neon- or any other noble gas-- the electron configuration of the previous noble gas can be abbreviated by the symbol for the noble gas in brackets EX: look at the picture

Light: Color of Light

- white light, as produced by the sun or by a light bulb, contains a spectrum of wavelengths & therefore a spectrum of color a) we see these colors-- red, orange, yellow, green, blue, indigo, & violet- in a rainbow or when white light is passed through a prism b) red light, with a wavelength of 750 nm (nanometers) has the longest wavelength of visible light c) violet light, with a wavelength of 400 nm, has the shortest wavelength of visible light (1 nm= 1 X 10^-9 nm) - the presence of color in white light is responsible for the colors we see in our everyday vision

Models that explain the inertness & reactivity of the elements

-Are other elements as reactive as hydrogen? a) the reactivity exhibited by hydrogen is also seen in other Group 1 elements, such as lithium & sodium -the inertness of helium is seen in Ne, Ar, & the other noble gases -Mendeleev's periodic law sums up these observations: when the elements are arranged in order of increasing atomic number certain sets of properties recur periodically. a) models & theories help explain the observed behaviors of groups of elements such as the Group 1 metals & noble gases

Blimps, Balloons, & Models of the atom

-on May 6, 1937, while landing in New Jersey on its first transatlantic crossing, the Hindenburg burst into flames, destroying the airship & killing 36 of the 97 passengers -apparently, as the Hindenburg was landing, leaking hydrogen gas ignited, resulting in an explosion that destroyed the airship -the skin of the Hindenburg, which was constructed of flammable material, may have also been partially to blame for its demise -modern blimps are filled with helium, an inert gas a)the nucleus of the helium atoms has 2 protons, so the neutral helium atom has two electrons- a highly stable configuration

Blimps, Balloons, & Models of the atom (questions)

-what is it about helium atoms that makes helium gas inert? -by contrast, why is hydrogen so reactive? a) elemental hydrogen exists as a diatomic molecules b) H2 atoms are so reactive that they react with each other to form hydrogen molecules -what is it about hydrogen atoms that make them so reactive?