Ch 1 - Atomic Structure Flashcards
The study of Atomic Structure
To calculate the atomic mass of a number, what do you need to know?
The number of stable isotopes of the element, the mass of each isotope, and the natural percent abundance of each isotope.
define the term atomic number of an element?
the number of protons in the nucleus of an atom
What is an Atom?
- Atoms are the smallest particles of an element that have the chemical properties of that element.
- All atoms consist of three particles, called protons, neutrons and electrons.
- Each atom has a nucleus at approximately the centre of its volume consisting of the two types of particles called protons and neutrons.
- The nucleus of an atom is positively charged.
- Electrons are distributed around the volume of the atom of which they are a part in “shells”, “orbits” or “energy levels”
In 1913, Niels Bohr suggested an explanation for the emission spectrum by proposing a model for the hydrogen atom. What did he propose?
- He proposed that electrons of specific energy move around the central nucleus in circular orbits or energy levels.
- Electrons cannot exist between these orbits
- Although an electron cannot lose energy while orbiting a nucleus, it could be given excess energy (by a flame or electric current) and then move to a higher orbit. If this happens, the electron has moved from the ground state (lowest energy level) to an excited state.
- When it drops back down to a lower, more stable orbit, this excess energy is given out as a photon or quantum of light. This is seen as a line of a particular colour on the visible spectrum.
What are 5 Problems with the Bohr Model?
- It violates the Heisenberg Uncertainty Principle because it considers electrons to have both a known radius and orbit.
- The Bohr Model provides an incorrect value for the ground state orbital angular momentum.
- It makes poor predictions regarding the spectra of larger atoms.
- It does not predict the relative intensities of spectral lines.
- The Bohr Model does not explain fine structure and hyperfine structure in spectral lines.
- It does not explain the Zeeman Effect.
List of 5 important facts about Compounds.
- Compounds consist of molecules formed from atoms of 2 or more different elements bound together chemically.
- Compounds can be broken down into a simpler type of matter (elements) by chemical means; not by physical means
- Compounds always contains the same ratio of component elements.
- Compounds have properties different from their component elements
- e.g. the compound water (H2O) is a liquid at room temperature and pressure and has different chemical properties from those of the two elements, hydrogen (H2) and oxygen (O2), from which it is formed.
- Compounds can be represented using chemical formulae.
- Draw a diagram to show the arrangement of carbon atoms in a diamond crystal.
Do all covalent bonds conduct electricity?
NO (except graphite and graphene)
- Diamond, graphite and silicon dioxide are all examples of giant covalent structures. What does the word giant mean in this context?
- it continues on and on in three dimensions.
- Draw a diagram or diagrams to show the arrangement of carbon atoms in a graphite crystal.
Give 3 examples of a giant covalent structure
- Graphite
- Diamond
- SiO2
What is electrical current?
The movement of charged particles such as ions or electrons in a circuit.
Whose experiments were to find the quantity of charge carried by an electron?
Robert A. Millikan started his work on electron charge in 1906 and continued for seven years. His 1913 article announcing the determination of the electron’s charge is a classic and Millikan received the Nobel Prize for his efforts.
- What is electron configuration?
- The arrangement of electrons in the shells is called the atom’s electron configuration
- The electron capacity of each shell is limited.
- The maximum number of electrons that each shell can hold is 2n2 where n is the shell number or energy level.
- Electron shells are filled in order from the nucleus, starting with the K shell, so that the electrons are in their lowest possible energy levels (or ground state).
What are some Key Facts about Electrons?
- Electrons exist in the volume of atoms that surrounds the nucleus (see the diagram of an atom, on the right) and not in the nucleus of atoms - which is where the protons and neutrons are located.
- Electrons are therefore subatomic particles but they are not nucleons.
- Electrons have a negative charge of -1.
- An electron has a mass approximately 1/1836 of the mass of a proton, so a relative mass of 1/1836 ≈ 0.0005 ≈ zero. Electrons therefore account for very little of the total mass of the atom of which they are a part.
- The number of electrons in an atom is the same as the number of protons in the atom. That is because atoms are charge neutral, and protons have a charge of +1 while electrons have a charge of -1 so there must be the same number of each in order for the whole atom to be charge neutral. Recall that the number of protons in an atom is the atomic number of that atom (element).
How do you know how many electrons are in an element based upon what you see in the periodic table?
Check the atomic number, there are equal protons and electrons
When was the electron discovered? and
Who discovered the electron?
The electron was discovered in 1897 by British physicist J.J. Thomson who was working with Cathode Rays at the Cavendish Laboratory, Cambridge University.
Are electrons positively charged or negatively charged?
Negatively charged.
Elements are different because they contain different numbers of _______.
protons
Elements of the same period have the same number of
Electron shells
Elements such as O2 and Br2 are…
Diatomic molecules
Elements with the same group have the same number of…
Electrons in the outer shell
List 4 important facts about Chemical Elements.
- Elements consist of only one type of atom - which may, or may not be joined together to form molecules or large structures, so …
- Elements can exist either as atoms (e.g. argon) or as molecules (e.g., nitrogen)
- Elements cannot be broken down into a simpler type of matter by either physical or chemical techniques - though some larger elements break-down spontaneously due to being radioactive.
- Elements are listed in the periodic table.
What is meant by Energy State in Chemistry?
The position and energy of an electron described by its quantum numbers is known as its energy state.
Explain how an ionic compound forms (using the example of magnesium and chlorine to form MgCl2)
When magnesium atoms react with each chlorine atoms the magnesium atoms lose two electrons forming Mg2+ because it gives them to each of the two chlorine atoms, that gain one electron, each forming 2 Cl- ions
explain why atoms of an element may have different mass numbers?
they may have different numbers of neutrons
What does the Heisenberg Uncertainty Principle state?
The Heisenberg uncertainty principle states that it is impossible to know simultaneously the exact position and momentum of a particle. That is, the more exactly the position is determined, the less known the momentum, and vice versa.
how are ions detected in a mass spectrometer?
when the positive ions collide with the detector, they accept an electron which generates an electrical current.
How are metals good conductors of heat?
If you heat one end of the metal the energy is picked up by the delocalised electrons and as the electrons move around in the metal the heat energy is transferred throughout the structure.
How are the layers in graphite easily removed?
Although the forces holding the atoms together in each layer are very strong, the actual forces between the layers are much weaker. The layers are relatively far apart.
How can compounds form?
Energy transfer
How can you break an ionic compound?
Provide enough energy
How do you know how many protons are in an element based upon what you see in the periodic table?
Check the atomic number
How do you work out the number of shells with the period number?
Moving across each period, you can see that the number of shells is the same as the period number. For example if it is the 1st period then it will only have 1 shell or if it is the 4th periods it will have 4 shells.
How does one calculate the atomic mass of a number?
Multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.
How many bonds can an atom form?
As many bonds as there are electrons in its outermost shell.
How many carbon atoms is each carbon atom bonded to in graphite and what does this mean?
3, that there is a delocalised electron
How many electrons are you allowed on the 3rd shell?
8
How many other carbon atoms is each carbon atom bonded to in diamond?
4
How would you draw an ionic structure, e.g. NaCl
Draw two particles in the key, e.g. Na+ as a black dot and Cl- as a blank dot.Draw lots of cubes with a particle on each corner, make sure there are never any two Na+ connected by lines and visa versa.
What does Hund’s Rule state?
- Every orbital in a sublevel is singly occupied before any orbital is doubly occupied.
- All of the electrons in singly occupied orbitals have the same spin.
identify the block in the periodic table to which magnesium belongs?
s block
If oxygen gains 2 electrons through ionic bonding will it be (2-) or (2+)? Why?
(2-) because electrons have a negative charge.
in a mass spectrometer, why is it necessary to ionise atoms before acceleration?
if the particles are not charged they cannot be attracted to and accelerated by a charged plate
In a simple molecule what do you have to break to melt the substance?
Intermolecular forces of attraction
Ion
An atom that loses or gains an electron and changes its charge.
What is an ion?
An atom or group of atoms which carries an elecrical charge, either positive or negative.
Describe an ionic crystal shape
Giant three-dimensional regular lattice structure
Give an example of a giant ionic structure
Sodium chloride. NaCl
Is an atom more or less reactive with a full outer shell? Why?
LessBecause there is no room for reactions to take place if the outer shell is full.
Is graphite more or less dense than diamond? Why?
Graphite is less dense because the layers in graphite are relatively far apart. In a sense a graphite chrystal contains a lot of wasted space which there isnt in a diamond.
Is the atom more reactive with a full outer shell or less reactive?
Less reactive.
Because isotopes of an element have different numbers of neutrons, they also have different ____ _______.
mass numbers
Isotopes
For an element, multiple species of atoms with the same number of protons (same atomic number) but different numbers of neutrons (different mass numbers) exist; these are called isotopes of the element.Isotopes are referred to either by the convention described above or, more commonly, by name of the element followed by the mass number. Like carbon-12 and carbon-14.Almost all elements exist as a collection of two or more isotopes.
Isotopes are…
Atoms with different numbers of neutrons e.g. Chlorine
What are the main points of John Dalton’s Atomic Theory (1808)?
- The elements are made of atoms, which are tiny particles, too small to see.
- All atoms of a particular element are identical.
- Atoms of different elements have different properties: their masses are different, and their chemical reactions are different.
- Atoms cannot be created, destroyed or split.
- In a chemical reaction, atoms link to one another, or separate from one another.
- Atoms combine in simple whole-number ratios to form compounds
Key differences between mixtures and compounds:
• Compounds are in fixed proportions, mixtures aren’t.• In a mixture of elements, the elements still have their own properties. But elements in a compound will not retain the same properties.• Mixtures can be separated by physical means, for compounds you must change them chemically to separate them.• There are no energy changes involved in a mixture where as when compounds are made energy is released.
Li 3 7 If you have lithiums structure like this, how many electrons will be on the outer shell?
1 on the outer shell
Magnetic Quantum Number (ml)
Third quantum number. Describes the orientation of the orbital in space. An orbital is a specific region within a subshell that may contain no more than two electrons. THe magnetic quantum number specifies the particular orbital within a subshell where an electron is highly likely to be found at a given point in time. The possible values are all integers from l to -l, including 0. Therefore, the s subshell, where there is one possible value of ml (0), will contain one orbital; likewise, the p subshell will contain three orbitals, the d subshell will contain five orbitals, and the f subshell will contain seven orbitals. The shape and energy of each orbital are dependent upon the subshell in which the orbital is found. For example, a p subshell has three possible ml values (-1, 0, +1). The three dumbell shaped orbitals are oriented in space around the nucleus along the x, y, and z axes and are often referred to as px, py, and pz.
define the term mass number of an element?
the total number of protons and neutrons in the nucleus of an atom
What is the Mass Number of an atom?
The Mass Number of an atom is the total number of
protons and neutrons it contains (all of which are located in the nucleus of the atom).
- The Mass Number of an atom is represented by the symbol A.
- The Mass Number of an atom is also known as the Nucleon Number.
Describe the diagram of a metallic bond
Layers of positively charged ions surrounded by a ‘sea’ of delocalised electrons Layers of ions in a giant structurei.e. circles with plus signs in with a label around saying sea of delocalised electrons
What is ‘the mole’ in chemistry?
- IThe “mole” is a number scientifically determined such that when you have 1 mole of nucleons (either protons or neutrons or both), it weighs exactly 1 gram. There is a near perfect correlation between the total number of nucleons in an atom and how many grams 1 mole of those atoms weighs.
- The number is Avogadro’s number (constant) , 6.022 x 1023 particles.
For example, the atomic weight of carbon is 12.0g/mol, which means that 6.022x1023 carbon atoms weigh 12.0g.
Give an example of a simple molecular structure
H2O
What are the properties of simple molecular structures?
- Contain only a few atoms held together by strong covalent bonds - An example is carbon dioxide (CO2), the molecules of which contain one atom of carbon bonded with two atoms of oxygen.
- Low melting and boiling point - This is because the weak intermolecular forces break down easily.
- Non-conductive - Substances with a simple molecular structure do not conduct electricity. This is because they do not have any free electrons or an overall electric charge.
- Tend to be insoluble to water - Those which do dissolve often react with the water, or else are capable of forming hydrogen bonds with the water.
- Often soluble in organic solvents
What is a molecule?
- A molecule is a group of atoms held together by covalent bonds
- A molecule is the smallest unit (particle) of a compound that has the physical and chemical properties of that compound.
How do you calculate the Relative Atomic Mass (Ar) (Atomic Weight) of an element?
The relative atomic mass (Ar) of an element represents the average mass of one atom, taking into consideration the number of isotopes of the element, their relative isotopic mass (RIM) and their relative abundance. Using data from the mass spectrum, one could calculate the relative atomic mass for an element by using the following method of calculation:
- What is the Atomic Number?
- What is the Mass Number?
- How is an element recorded on the periodic table?
- What is an Isotope?
- The atomic number (symbol Z) is the number of protons in the nucleus of an atom.
- The mass number (symbol A) is the number of protons and neutrons added together.
- See Image
- An isotope is a form of an element with the same number of protons but different numbers of neutrons in the nucleus
