CHM 1020C Lecture 3

If the number of electrons is less than the number of protons, the atom is a

CATION

it is a perfect technique for working with dirty mixtures of samples which are often the only kind available at a crime scene.

Mass spectrometery

had deduced that the energy of the photons comprising EM (electromagnetic) radiation is a function of its frequency (E = hν), this Planck's equation.

Max Planck

stated that the structure of an atom had specific energy levels in which the electrons were located around the nucleus

Neils Bohr

Are large and heavy like protons except they have no electrical charge

Neutrons

Provide the "extra Glue" that hold the nucleus together

Neutrons

an extra attractive force that belongs in nucleus that works only between protons and neutrons ; without this force the nucleus would disintegrate

Strong nuclear force

Oxygen also exists as O3 = ozone. This is called an

allotropic forms

Bohr also assumed that the electron can change from one

allowed orbit to another

So through Bohr's equation we can relate the energy to the structure of the

atom

Since the number of protons for a specific element is always the same and given by the atomic number, calculating the number of neutrons in an atom is easy; just subtract the number of protons from the

atomic mass number

Each element has a unique

atomic number

makes statements regarding chemical changes much easier

chemical symbols

Hydrogen isotope with one proton and one neutron

deuterium

Different elements have BLANK so that is why different elements emit or absorb different amounts (wavelengths) of light.

different energy levels

an increase in frequency increases the

energy of the photons created.

Those clouds are located specific distances from the

nucleus

an increase in intensity just increases the

number of photons created

electrons live in shells that are wrapped around the nucleus called

orbitals

Only electrons in the blank orbitals participate in chemical reactions these are called valence electrons

outer

The atom is composed of three types of

particles

as each electron moves from a higher energy level (orbit) to a lower one, a different color is emitted. The numbers shown above the colors are the wavelengths that correspond to the color.

the Bohr model

The protons and neutrons are located in center of an atom called

the nucleus

If two protons are in the nucleus they will fly apart because they have

the same charge

The relationship between wavelength and frequency is related through

the speed of light c=λν

Through Planck's equation we can relate the frequency of light to the

energy

The unit used most often to describe frequency is Blank which means "per second" or /s.

(Hertz) Hz

Wavelengths found in the electromagnetic spectrum (range of light) can be measured in units a small as

10^-11 meters (gamma waves)

Wavelengths found in the electromagnetic spectrum (range of light) can be measured in units as large as

10^3 Meters (radio waves)

If the number of electrons is greater than the number of protons, the atom is an

ANION

The number of neutrons plus the number of protons is called the

ATOMIC MASS NUMBER

The number of protons in an atom is called the

ATOMIC NUMBER of the element

Are the fundamental units of matter

Atoms

1. Electrons assume only certain orbits around the nucleus. These orbits are stable and called "stationary" orbits.

Bohr Model Principle 1

2. Each orbit has an energy associated with it. For example the orbit closest to the nucleus has an energy E1, the next closest E2 and so on.

Bohr Model Principle 2

3. Light is emitted when an electron jumps from a higher orbit to a lower orbit and absorbed when it jumps from a lower to higher orbit.

Bohr Model Principle 3

4. The energy and frequency of light emitted or absorbed is given by the difference between the two orbit energies, e.g.

Bohr Model Principle 4

1.The electrons were emitted immediately. 2. Increasing the intensity of the light increased the number of photoelectrons, but not their maximum kinetic energy. 3. When Na is the metal red light will not cause the ejection of electrons, no matter what the intensity. 4. Weak violet light will eject only a few electrons, but their maximum kinetic energies are greater than those for intense light of longer wavelengths.

Characteristics of Photoelectric effect

are formed by the combination of atoms

Compounds

Compounds that share electrons are

Covalent Bonds

In the 5th century B.C. a philosopher hypothesized that all matter (plus space and time) is composed of tiny indestructible units, called atoms named

Democritus

can be used to "label" compounds that have hydrogen atoms so that the spectroscope can see their location better. Because of the additional mass of the extra neutron in the nucleus, this makes the atom easier to "see".

Deuterium

Atoms are overall neutral meaning the positive charge of a proton need to be cancelled by the negative charge of a

Electron

The number of BLANK in each orbital are very important because they effect the properties of the element and how it will behave in the world i.e. lithium is a metal because it has one electron in its outer orbital

Electrons

are tiny, very light particles with a negative charge

Electrons

In the case of light, BLANK refers to the number of times a wavelength is repeated per second

Frequency

is the number of occurrences of a repeating event per unit time.

Frequency (ν)

Monatomic Elements called noble gases used to be called inert gases

Helium, Neon, Argon, Krypton, Xenon, and Radon

the only atom that does not need a neutron in its nucleus because it has one proton and one electron

Hydrogen

is similar to UV/VIS spectroscopy in that it uses light to determine the structural components in a substance, but unlike UV/VIS spectroscopy, the wavelength of Infrared light is not sufficiently energetic to cause an emission.

Infrared spectroscopy

it is the number of waves or photons of light reaching your detector; a brighter object is more intense but not necessarily more energetic.

Intensity

The variation in the number of Neutrons in an atom are called

Isotopes

use a stream of electrons to convert molecules or atoms into positive ions so that they can be attracted using a magnet.

Mass spectrometers

an energy particle (electromagnet radiation) called a

PHOTON

NO TWO ELEMENTS HAVE THE SAME NUMBER OF

PROTONS IN THEIR ATOMS.

We can use the light that passes through the sample and is not absorbed to not only confirm the presence of our molecule in a sample but also quantify how much of the compound is present based on the response.

Photoelectric effect

Hydrogen isotope with one proton and no neutrons

Protium

Are much larger and heavier then electrons. These particles have a positive charge

Protons

The atomic number of an atom is always the same as the number of BLANK in its nucleus

Protons

The number of blank identifies the element

Protons

What makes up electromagnetic sprectrum

Radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays, and gamma rays

is defined as the distance between the crests or troughs of a wave motion.

The wavelength (λ) of light

It's been determined experimentally that when light shines on a metal surface, the surface emits electrons. This is called the photoelectric effect.

This is called the photoelectric effect.

Hydrogen isotope with one proton and two neutrons

Tritium

is also used for determining the concentration of illegal substances in mixtures

UV/VIS spectroscopy

are involved in the formation of chemical bonds between atoms

Valence electrons

The light we see color in

Visible Light

does lead to the rearrangement of atoms

a chemical reaction

If the electron gains energy this is called an

absorbance

Spectrometers like the one above can be set to read in two different units

absorbance (A) or percent transmission (%T).

Energy must be BLANK for an electron to move to a higher state (one with a higher n value)

absorbed

In both cases an energy particle called a PHOTON is absorbed or emitted and thus light is

absorbed or emitted

Energy is BLANK when the electron moves to an orbit of lower energy (one with a lower n value)

emitted

the second orbital can have only

eight electrons

range of light

electromagnetic spectrum

it is very important in determining the charge of the atom and how reactive the atom will be with the world around it.

electron

The number of electrons in each orbital is called the

electron configuration

emission spectrum is determined by

electronic structure

The wavelengths and frequencies of the light emitted by an atom (its emission spectrum) is determined by its

electronic structure.

Have almost no mass an orbit the nucleus at incredible speeds

electrons

are found in clouds that surround the nucleus of an atom

electrons

are located in energy levels surrounding the nucleus.

electrons

The overall shape of the shells depends on the number of

electrons in the atom

The higher the atomic number, the more shells and electrons an atom will have. The overall shell shape becomes more complex as the number of

electrons increases

The wavelengths and frequencies of the light emitted by an atom

emission spectrum

if it lost energy this is called an

emittance

In forensic investigations, the most common use of UV/VIS spectroscopy is the determination of i.e. if you have a chip of paint from an accident scene that you need to match to a suspect's car, you can use UV/VIS spectroscopy to determine the wavelength of maximum absorbance and that will give you the specific color of the paint chip for comparison.

exact colors.

When an electron Blank from a higher orbit to a lower one the energy difference is a defined amount and results in emitted electromagnetic radiation of a defined energy (ΔE)

falls

The overall change in energy associated with "orbit jumping" is the difference in energy levels between the

final and initial orbits:

The full electromagnetic spectrum is generally shown with both measurements given

frequency and wavelength

Whenever an electron moves from one of these energy levels to another it must either

gain or lose energy

Mass Spectrometry or IR spectroscopy, are used to confirm the identification of the

illegal substance.

But if the number of electrons is greater or less than the number of protons, then you have what is called an

ion

Compounds that are held together by difference in charge are

ionic bonds

Electrons are the glue that hold together

molecules

For the wavelengths of visible light (the light we see in color) the most common units used

nanometers and Angstroms

In an atom where the number of electrons is exactly the same as the number of protons, the atom is said to be

neutral

is an uncharged particle that is also found in the nucleus of atoms

neutron

Neutrons are found in all atoms that have one more than one

proton

The number of blank and blank must be the same; this is true for all atoms

protons and electrons

Atoms are made up of three subatomic particles

protons, neutrons, and electrons

Planck's equation implies the higher the frequency of a radiation, the more energetic are its

quanta

radiant energy is emitted in small bursts, known as

quanta

Because electrons move so BLANK it is impossible to know the exact location of the electron around the nucleus

quickly

One of the main ways forensic scientists and chemists analyze the data they collect is by using a piece of equipment called a

spectrometer

Isotopes are important because we can often use them in

spectroscopy

The most inner orbital can only have

two electrons

each element has its own

unique symbol

photon's energy depends on the

wavelength (or frequency) only

In the case of light, frequency refers to the number of times a

wavelength is repeated per second.