Chemistry CH 2

First row elements (period 1) electron configurations

-The atomic number tells us how many electrons must be placed in orbitals Hydrogen= 1s^1= one electron in the 1s orbital Helium= 1s^2= Two electron in the 1s orbital

Rules to determine the Ground State Electronic Configuration of an Atom

#1--Electrons are placed in the lowest energy orbitals beginning with the s orbitals (2s and 3s= the orbital closer to the nucleus is lower in energy thus the energy of 2s orbital is lower than the 3s orbital)(Shell= increased orbital energies in the following order: s.p,d,f) (Energies in first three periods: 1s, 2s, 2p, 3s, 3p and above this all other orbitals of one shell do not have to be filled before any orbital in the next higher shell gets an electron) #2--Each Orbital holds a maximum of 2 electrons #3--When orbitals are equal in energy, one electron is added to each orbital until the orbitals are half filled, before any orbital is completely filled (1 electron is added to three p orbitals before filling any p orbital with two electrons)(because like charges repel each other, adding electrons to different p orbitals keeps them further away from each other, which is energetically favorable ---Orbital Diagrams use a box to represent each orbital and arrows to represent electrons. A single electron- unpaired electron- is an arrow up. Two electrons in a orbital have paired spins, so the spins are opposite in direction, so up and down arrows are used. --The periodic table can be used to determine the electron configuration of an element

The Periodic Table

(1-7) Labeled Periods: (horizontal rows) 18 Columns (Vertical Columns) -A row: a period. Elements in same row= similar in size -A column: a group. Elements in same group= similar electronic and chemical properties -Lanthanides= z= 58 & Actinides= z=90 -Group Number: How each column of the period table is assigned. -Main group Elements: consist of two columns on the far left and six columns on the far right of the table -Transition Metal elements: contained in the 10 short columns in the middle of the table (3-12 or 1B-8B) -Inner transitional Metal elements: consist of lanthanides and actinides, and they are not assigned group numbers

Compounds

- A compounds is a pure substance formed by chemically combining two or more elements together -A chemical Formula uses element symbols to show identity of the elements forming a compound and subscripts to show the ratio of atoms contained in the compound Examples: H2(subscript)O = 2 H's for each O CO2(subscript) = 2 O's for each C C3(subscript)H8(Subscript) = 3 C's for each 8 H's Go to Figure 2.3 to see common elements used in molecular art for future problems

Structure of an Atom

--Atom is a building block that is what encompasses all mater --Atom is composed of three subatomic particles: 1. A proton symbolized by p, has a positive charge 2. An electron, symbolized by e-, has a negative charge 3. A neutron, symbolized by n, has no charge -Protons and neutrons are about the same exceedingly small amount of mass. -The mass of electrons is less, 1/1,836 of the mass of a proton -Subatomic particles are not evenly distributed in the volume of an atom --Two main components of an Atom: 1. The nucleus is a dense core that contains the protons and neutrons. Most of the mass of an atom resides in the nucleus 2. The electron cloud is composed of electrons that move rapidly in the almost empty space surrounding the nucleus. The electron cloud comprised most of the volume of an atom *Diameter of an atom= 10^-10m, the diameter of the nucleus= 10^-15* -The charged particle of an atom can either attract or repel each other - Opposite charges attract while like charges repel each other *2 electrons/ 2 protons= repel *Proton and a electron= attract Atom mass= 10^-24g so chemists use a standard mass: --Atomic mass Unit, which defines the mass of an individual atom relative to its standard mass --One Atomic Mass Unit (amu) = 1/12th the mass of a carbon atoms that has 6 protons and 6 neutrons; 1amu=1.661 x 10^-24 --One proton= 1.0073 amu, One neutron= 1.0087 amu, One electron= a mass so small it is ignored Each atom of an element has the same number of protons in the nucleus, a value called the atomic number, symbolized by Z. Different elements have different atomic numbers --The atomic number (Z)= the number of protons in the nucleus of an atom --Hydrogen has one proton in its nucleus, so Z=1 --The periodic table is arranged in order of increasing atomic number beginning at the upper left hand corner. --Atomic number appears just above the element for each entry on the table --Z= the number of protons in Nucleus= The number of electrons --Atomic number= # of protons in nucleus and # of electrons in its cloud

Unusual Nature of Carbon

--Has three elemental forms: Diamond (dense three dimensional network of carbon atoms in 6 membered rings), Graphite (Slippery black and used as lubricant, has parallel sheets of carbon atoms in flat 6 membered rings), Buckminsterfullerene (60 carbon atoms in a sphere of 20 hexagons and 12 pentagons resembling a soccer ball) --Its ability to join itself and other elements gives it versatility not seen with any other element in the periodic table

Atomic Weight

--The atomic weight is the weighted average mass of the naturally occurring isotope of a particular element reported in atomic mass units --Two quantities must be known to determine the atomic weight: the mass of each isotope in atomic mass units, and the abundance with each isotope occurs How to determine the Atomic Weight of an Element? 1. List each isotope in amu and the percentage that each one occurs in nature, convert the percentage to a decimal ex: 35CI: 34.97 (amu); 75.78% = 0.7578 (Isotopic abundance) 37CI: 36.97 (amu); 24.22% = 0.2422 (Isotopic abundance) Multiply the isotopic abundance by the mass of each isotope, and add up the products. The sum is the atomic weight for the element: 35CI: .7578 x 34.97amu = 26.5003 amu 37CI: .2422 x 36.97 amu = 8.9541 amu Atomic Weight (added sums)= 25.4544 amu = 35.45 amu Isotopes in Medicine: -Generally, the chemical properties of isotopes are identical -Sometimes one isotope is radioactive (emits particles or energy in a form of radiation) -Radioactive isotopes have both a diagnostic and therapeutic use in medicine

Valence Electrons

--electrons in the outermost shell are loosely held, are the chemical properties of an element. The period number tells the number of valence shell Relating Valence electrons to group numbers: --To identify valence electrons, look for the shell with the highest number CI= 2 electrons in 3s orbital and 5 electrons in the 3p orbital= 7 valence electrons --Elements in the same group have the same number of valence electrons and similar electronic configurations --The group number (using 1A-8A system) equal the number of valence electrons for the main group elements (except helium): each element in 1A has one electron in an S orbital. The period number indicates the valence shell number --This the periodic table is organized into groups of elements with similar valence electronic configurations in the same column. --The chemical properties of a group are similar because these elements contain the same electronic configuration of valence electrons --Filled valence shells are the noble gases (8A). Their valence configuration starts with helium (1s^2) the remaining elements have filled s and p orbitals (s^2p^6) -The group number of a main element= the number of valence electrons + the period number equals how many shells

Electron- Dot Symbols

--represent the valence electrons as dots placed on the sides of a symbol. --Each dot represents one valence electrons --The dots are placed on the four sides of an element --For one to four valence electrons, single dots are used. With more than 4 electrons, the dots are paired

Characteristics of Groups 1A, 2A, 7A, 8A

-Elements that comprise a particular group have similar chemical properties --Alkali Metals (Group 1A) and Earth Elements (Group 2A): 1. Located on far left and right side of the table 2. Group 1A: Soft & shiny, low melting points, good conductors of heat & electricity, react w/ water to form basic solutions 3. Group 2A: Shiny solids, less reactive than alkali metals 4. Groups 1A & 2A don't exist in nature as pure elements, rather they are combined to form compounds --Halogens (group 7) and Noble gases (group 8A) 1. located on far right side of table 2. Halogens (7A/ group 17): in elemental form, they contain two atoms joined together(F2). Are very reactive and combine with many other elements to form compounds 2. Noble Gases (8A/ Group 18): Stable atoms especially & rarely combine with other element to form compounds

Using the Atomic Number and Mass number to determine the number of protons, neutrons, and electrons

-How many protons and Neutrons in argon. Atomic number=18 and a mass number of 40 Analysis: -In a neutral, atomic number (Z)= the number of protons= the number of electrons. -The mass number (A)= the number of protons + the number of neutrons Solution: Z= 18 so Argon has 18 protons and 18 electrons. To find the number of neutrons, subtract the atomic Number from the atomic mass: 40-18= 22 neutrons

Electronic Configurations of Other elements Using the periodic table

-How to use the location of an element in the periodic table to determine what orbitals are filled with electrons -4 regions called blocks that are labeled according to the subshells that are filled with electrons last: s, p, d, and f. -S Block: 1A & 2A and the element helium. The sub subshell is filled last in these elements -P block: 3A-8A (except for helium) the P shells are filled last in these elements -D block consists of 10 columns of transitional metals. The D subshells are filled last in these elements -F block consists of two groups of 14 inner transitional metals. The F subshell is filled last in these elements Draw Orbital diagram for the ground state electronic configuration of an element Ex) Sulfur 1---Use the atomic number to determine number of electrons. Sulfur=16 electrons that must be placed in orbitals 2---Locate element on periodic table and determine orbital filling by: -Row by Row read from left to right beginning at the left upper corner and ending at the element in question. :1s, 2s, 2p,3s, 3p 3----Give each orbital two electrons until all electrons are used. in filling the orbitals of the same energy, place electrons one at a time in the orbitals until they are half filled -add 2 electrons to each of: 1s, 2s, three 2 p, and 3 s orbitals (12 electrons used) -Add remaining 4 electrons to the 3p orbitals, give one orbital 2 electrons and place one unpaired electron in the remaining 2 orbitals: 1s^(2)2ps^(2)2p^(6)3s^(2)3p^(4)

Electronic Structure

-The chemical properties of an element are determined by the number of electrons in an atom -Electrons do not move freely in space, rather an electron is confined to a specific region, giving it a particular energy -Electrons occupy discrete energy levels. The energy of electrons is quantized ; that is, the energy is restricted to specific values Principal Energy Levels OR Shells: -- Shells are numbered: n= 1,2,3,4 and so on beginning closest to the nucleus --Electrons closer to the nucleus are held more tightly and are lower in energy --Electrons farther from the nucleus are held less tightly and are higher in energy --n value= determines number of electrons that occupy a shell --The further the shell is from the nucleus, the larger its volume becomes, and the more electrons it can hold --First shell= 2 electrons, the second holds 8, the third holds 18. --Maximum number of electrons= 2n^2 n= the shell number --Subshells are what is inside shells and is identified by s, p,d and f. The subshell consists of orbitals --An orbital is a region of space where the probability of finding an electron is high. Each orbital can hold 2 electrons --A particular type of subshell contains a specific number of orbitals: s= 1 s orbitals; p= 3 p orbitals; d= 5 d orbitals; f= 7 f orbitals. - The number of subshells in a shell is equal to the value of n --First shell of electrons around a nucleus (n=1) has only 1 s orbital (1s)= First shell can hold 2 electrons --2nd shell of electrons (n=2) has two types of orbitals (2s, 2p)= 2 electrons per orbital and there is 4: the second shell can hold 8 electrons --Third shell of electrons (n=3) has three types of orbitals one s, three p, and 5 d orbitals (3s, 3p, 3d- locate din third shell): there are 9 total orbitals and each can hold 2 electrons, so the third shell can hold 18 electrons --The fourth shell (n=4) has 4 types of orbitals: one s, three p, 5 d, and seven f orbitals. We are in 4th shell so they are known as: 4s, 4p, 4d, 4f. there are 16 orbitals and each one can hold 2 electrons, so the fourth shell has 32 electrons --The maximum # of electrons in a shell is determined by the number of orbitals in a shell --Each orbital has a particular shape: -s orbital: a sphere of electron density. it is lower in energy than other orbitals in the same shell because electrons are kept closer to the positively charged nucleus -A p orbital has a dumbbells' shape. A p orbital is higher in energy than an s orbital in the same shell because its electron density is farther from the nucleus --All s orbitals are spherical but they increase in size as the shell number increases

Using an Isotope symbol to determine the number of protons, neutrons, and electrons?

-The superscript= Mass number (help to find neutrons) and the subscript= Atomic Number (used to find protons/ place on periodic table) -Atomic number= number of protons= electrons -Mass number= number of protons+ number of neutrons

2nd row elements( period 2) electron configurations

-Use the 4 orbitals in the second shell- 2s & 2p orbitals -1s orbitals are filled with electrons and the remaining are added to the orbitals in the second shell. -Since the 2s orbital is lower in energy than the 2 p orbitals, it is completely filled before adding electrons to the 2 p orbitals Lithium(Z=3-3 electrons) 1s= 2 electrons, 2s orbital= 1 electron, unpaired Lithium's Electron configuration: 1s^(2)2s^(1) Carbon(Z=6- electrons): 1s & 2s orbitals= 2 electrons each. The remaining 2 are added to two different 2 p orbitals, giving carbon 2 paired electrons. Electrons spin in the same direction, upwards: Carbons electron configuration: 1s^(2)2s^(2)2p^(2) Oxygen (Z=8 electrons) 1s & 2s = 2 electrons each, 2p orbital= 4 electrons- 3 arrows up, 1 downwards. Oxygen now has 2 unpaired electrons Oxygen's electron configuration: 1s^(2)2s^(2)2p^(4) Neon: (z=10) 1s &2p= 2 electrons each, Each of the three 2p=6 electrons in total Second shell is completely full: 1s^(2)2s^(2)2p^(6) -Sometimes electron configuration is shortened by using the noble gas that has a filled shell of electrons from the proceeding row, and then adding the electronic configuration of all the remaining electrons using orbitals and superscripts For example w/ Helium (1s^(2)): Carbon: [He]2s^(2)2p^(2)

Ionization Energy

-energy is required to remove an electron from a neural atoms because a negatively charged electron is attracted to a positively charged nucleus -The more tightly it is held, the greater the energy needed to remove it. -Removing an electron from a neural atoms forms a cation -Ionization energy is the energy needed to remove an electron from a neural atom -Cation is positively charged, and has fewer electrons than a neural atom -Ionization energies decrease down a column of the periodic table as the valence electrons get further away from the positively charged nucleus -Ionization energies generally increase across a row of the periodic table as the number of a protons in the nucleus increases -Further to the left and furthest down= largest atomic radius -Farthest to the right and closest to the top= higher ionization energy

Identifying Elements in Molecular Art example in book (41)

1. See the figure given to you 2. Determine the identity of the color coded spheres 3. Solution A. the blue spheres= nitrogen & red spheres= oxygen. This one particle has 2 nitrogens , and one contains 2 oxygens and two contain one oxygen and one nitrogen B. This ball and stick representation contains the elements carbon (black) nitrogen (blue) and hydrogen (gray)

An element?

An element is a pure substance that cannot be broken down into simpler substances -188 known -90 are naturally occurring -28 are prepared in a laboratory Each element is defined by one or two letter symbols -While most are derived from one or two letters of the elements name, 11 elements have symbols derived from Latin or German Origins

Atom

Greek word: Atomos: "unable to cut"

Isotopes

Isotopes: Atoms of the same element that have different numbers of neutrons -Number of neutrons can vary in atoms of elements -Most elements in nature are a mixture of isotopes, like chlorine has 17 protons but can have 18 or 20 neutrons! (Chlorine-35 & Chlorine-37) -An isotope symbol is also written using the element symbol with the atomic number as a subscript and the mass number as a superscript, both to the left -Sometimes the subscript is omitted --Hydrogen= 3 isotopes: Deuterium= hydrogen with a mass of two (D) (1 proton, 1 neutron) Tritium= hydrogen with a mass of three (T) (one proton, 2 neutrons)

Mass Number

Mass number (A)= the number of protons (z) + the number of neutrons

Period Trends

Periodic Trends: They change in a regular way across a row or down a column on the periodic table: Atomic size & ionization energy Atomic Size: Size is measured by atomic radius, distance from nucleus to the outer edge of its valence shell -The size of atoms increases down a column, as valence electrons further from the nucleus (shells further in amounts as periods elements are in increase) --The size of atoms decrease across a row of the periodic table as the number of protons in the nucleus increases. An increasing number of protons pulls the electrons closer to the nucleus, so the atoms get smaller

Elements and the periodic Table

Periodic table: A schematic way elements are arranged based off of their similar properties. Its position reveals a lot of it chemical properties Three categories: Metals (located left of the line that begins with boron and ends with astatine) , nonmetals (located all to the right of the line except hydrogen), and metalloids (located along the steps of the line) Metals: Are Shiny materials that are good conductors of heat and electricity. All metals are solids at room temperature except for Mercury, which is a liquid Nonmetals: Do not have a shiny appearance, and they are generally poor conductors of heat and electricity. Nonmetals like sulfur and carbon are solids at room temperature; bromine is a liquid; and nitrogen, oxygen, and nine other elements are gases. Metalloids: Have properties intermediate between metals and nonmetals. Only 7 elements are categorized at metalloids: boron (B), Silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium (Te), and astatine (At)

Focus on the human Body

four nonmetals: oxygen, carbon, hydrogen, and nitrogen- comprise 96% of the mass of the human body and are called the building block elements -Hydrogen + oxygen= water - Carbon, hydrogen, and oxygen are found in proteins, carbohydrates, lipids, and nucleic acids -Major Minerals or Macronutrients present in smaller amounts in the human body: 0.1-2% by mass -Sodium, potassium, and chlorine are present in body fluids -Magnesium and sulfur occur in proteins, and calcium and phosphorus are present in teeth and bones -Phosphorus is in all nucleic acids (DNA) -100gm of each macronutrient is needed in the daily diet -Trace elements or Micronutrients required in diet in small quantities (less than 15mg)