2 What are Atoms?4th Century B.C. Democritus suggested that the universe was made of invisible units called atomsAtom Derived from Greek word meaning unable to be dividedHe thought that movements of atoms caused the changes in matter that he observed
3 John Dalton’s Atomic Theory Dalton also believed that atoms could not be dividedToday, we know that atoms are made up of much smaller particlesDalton’s theory:stated that all atoms of a given element were exactly alikeStated that atoms of different elements could join to form compounds** His theory is considered the foundation for the modern atomic theory
4 Atoms: The Building Blocks of Molecules An atom is the smallest part of an element that still has the element’s properties (chemical and physical)
5 What’s in an Atom?Atoms are made up of protons, neutrons, and electrons.The center of each atom is a small, dense NUCLEUS with a positive charge.Made of PROTONS and NEUTRONSProtons and neutrons are very similar in size and massThey differ because protons have a positive charge and neutrons have no electric charge.
6 What’s in an Atom? ELECTRONS move around the outside of the nucleus. These subatomic particles have a negative electric charge and have a very small mass.
7 What’s in an Atom? Unreacted atoms have no overall charge Atoms are not charged even though they are made up of charged subatomic particles.Due to equal number of protons and electrons
8 Models of the Atom Bohr’s Model He thought that electrons moved in set paths around the nucleus.Each electron has a certain energy that is determined by its path around the nucleusElectrons must gain energy to move to higher levels or lose energy to move to lower levels.
9 Models of the Atom A new model of the atom was proposed Stated that electrons behave like waves on a vibrating stringAn electron’s exact location cannot be determinedImpossible to determine both the exact location of an electron in an atom and the electron’s speed and location
10 Calculating Subatomic Particles Atomic number = 50Tells you how many protons are in an atomMass number = 118.7Sum of the numbers of protons and neutrons in the nucleus of an atom
11 Calculating Subatomic Particles How do you determine the number of electrons?The number of protons = the number of electrons the atomic numberHow do you determine the number of neutrons in an atom?The mass number – the atomic number = the number of neutrons.Remember: mass number = # of protons and neutronsatomic number = # of protons
12 Electrons Exist in Energy Levels The number of filled energy levels an atom has depends on the number of electrons.
13 Electrons: Found in Orbitals Within Energy Levels Orbital: A region in the atom where there is a high probability of finding electrons.Within each energy level, electrons occupy orbitals that have the lowest energy levels.There are four different kinds of orbitalsOrbitals s,p,d, and f
15 Orbitals S orbital P orbital Simplest and lowest energy level: hold 2 electronsSpherical shapeP orbitalHolds 6 electronsDumbbell shapeThree different orientations
16 Orbitals D orbital F orbital More complex 5 possible orbitals Has the greatest energy7 possible orbitals
17 Every atom has between 1 and 8 valence electrons A valence electron is the outermost energy level of an atom.Determine an atom’s chemical properties and ability to form bonds
18 Organization of the Periodic Table Periodic table groups similar elements together.The order of elements is based on the number of protons in the atom of elementsElements are arranged this way due to the periodic lawStates that when elements are arranged in this manner, similarities in their properties will occur in a regular pattern
19 Periodic Table Helps Determine Electron Arrangement Horizontal rows in the periodic table are called periods.The number of protons and electrons increase as you move across the periodic table from left to right
20 Elements In The Same Group Have Similar Properties Valence electrons determine the chemical properties of atomsElements in the same group or vertical column (up and down) have the same number of valence electrons
21 Some Atoms form IonsAtoms that do not have a filled s or p orbital may undergo ionization.They may gain or lose valence electrons in order to have a full outermost s and/or p ortbital.Atoms that gain or lose electrons no longer have an equal number of protons and electrons the ion forms a net electric charge
22 IONSRemoving an electron from an atom forms a positive ion, or a cation.Adding an electron to an atom forms a negative ion, or an anion.
23 How Do The Structure of Atoms Differ? Atomic number: Tells you how many protons are in an atomRemember that atoms have a neutral chargeWhat does this mean?Protons are equal to electronsMass Number: Equals the number of protons plus the number of neutronsAtoms of an element always have the same atomic number, but they can have different mass numbers
24 IsotopesAn isotope is an atom that has the same number of protons as other atoms of the same element but has a different number of neutrons.Some elements can have different versions of their atomEach atom has the same number of protons and electrons
25 The Mass of an Atom Atomic units are extremely small. Expressed in atomic mass units (amu).Atomic mass unit: A unit of mass that describes the mass of an atom or molecule. It is exactly one-twelfth of the mass of a carbon 12 atom.
26 The Mass of an AtomAverage atomic mass: the weighted average of the masses of all naturally occurring isotopes of an element.This is the number on the periodic table.More commonly found isotopes have a greater effect on the average than rare isotopes.
27 How Are Elements Classified? Classified into three groups:MetalsNonmetalsSemiconductors/Metalloids
28 Metals Characteristics ShinyCan be stretched and shapedGood conductors of heat and electricitySimilar metals are grouped together: there are different kinds of metals.
29 Metals Alkali Metals Found in Group 1 of the periodic table Highly reactive: only has one valence electronNot found in nature as elements they combine to form compoundsSoftShinyReacts violently with water
30 Metals Alkaline-earth metals Found in Group 2 Have two valence electronsCalcium: form hard shells of many sea animals, bones, and teethBe, Mg, Ca, Sr, Ba, and Ra
31 MetalsTransition metals: one of the elements in groups 3-12 on the periodic tableMuch less reactive than elements in groups 1 and 2.Can lose electrons to form cations (positive ions)Conduct heat and electricityShinyCan be stretched** Mercury (Hg) is the only metal that is a liquid at room temperature.
32 Synthetic Elements Technetium and promethium are man-made elements All elements with atomic numbers greater than 92 are man-made.
33 NonmetalsExcept for hydrogen, nonmetals are found on the right side of the periodic table.Include some elements in groups and all elements in groups
34 Nonmetals Carbon Found in three forms Graphite (pencil lead)DiamondFullerenesCarbon is found in both living and non-living thingsExamples: Glucose, chlorophyll, gasoline, and rubber tires
35 NonmetalsMany nonmetals gain electrons in order to have a full valence shell.Examples:Oxygen O2-Nitrogen N3-The most abundant gases in the air are the nonmetals nitrogen (N) and oxygen (O)
36 Halogens Halogens are located in group 17 of the periodic table. These elements are very reactive they need one electron to fill their valence shell.Just like the elements found in group one, these elements are not commonly found in nature. They are normally found in compounds.Elements: F, Cl, Br, I, At
37 Noble Gases Noble gases make up group 18. Elements in this group are different because they exist as a single atom instead of as molecules.These elements are inert or unreactive because the s and p orbitals are full of electrons.These elements do not gain or lose electrons to form ions.Elements: He, Ne, Ar, Kr, Xe, and Rn
38 Semiconductors Also called metalloids Only 6 elements: Boron Silicon GermaniumArsenicAntimonyTellurium
39 SemiconductorsSilicon atoms account for 28% of the mass of Earth’s crust