Atoms and the Periodic Table

Matter and Atoms Everything made of matter Matter has mass and volume Matter made of atoms Atoms are building blocks of matter Atoms cannot be chemically divided (H bomb - atoms going through a nuclear rxn, NOT a chemical rxn) Most matter made of compounds

Matter, Atoms, Compounds Compound: made of 2 or more types of atoms Ex: water: H 2 O made of 2 hydrogen atoms and 1 oxygen atom Learn later how compounds form Elements: basic substances of matter Element cannot be further broken down chemically Atom: smallest unit of an element that has the properties of the element Ex: hydrogen is an element, hydrogen atom is smallest unit of hydrogen you can find

Periodic Table of Elements Created by Dmitri Mendeleev in 1869 He noticed pattern of properties amongst elements when placed in order of atomic mass This order made problems in the pattern Today periodic table arranged by atomic number This better reflects patterns of properties

Periodic Table of Elements Neon Iodine Sodium Iron Sulfur Copper Boron

Periodic Table of the Elements Named periodic table b/c it’s periodic Regular repeating pattern in its arrangement Today it has many more elements than in 1869 New discoveries = new elements Atom is smallest whole unit of element

Organization of Periodic Table Vertical column = family or group Elements in group have similar chemical and physical properties Horizontal row = period Sides of table = main elements Middle of table = transition elements

Organization of Periodic Table Outline metals, nonmetals, metalloids (different colors)

Organization of Periodic Table Metals: solids (except mercury), ductile, malleable, conduct electricity, can make an alloy (combo of metals) Nonmetals: some solids, some liquid, some gas, most do not conduct electricity Metalloids: along “staircase”, hard to classify, properties of metal and nonmetal

Periodic Table Atomic symbol (ex. H = hydrogen) Atomic mass = number or protons & neutrons Atomic # = number of protons Na = sodium, Na is 11 so 11 protons; = 12 so 12 neutrons Atom electrically neutral (# protons = # electrons) Ex Na has 11 protons and 11 electrons

Periodic Table Row = period Period ends when highest energy level is full or 8 e- Noble gases: stable electron config., inactive/inert, Halogens: group #17, 7 valence e-, like to gain 1 electron to be happy Alkali metals: group #1, 1 valence electron, usually lose it to be stable

Atoms and Electrons Atoms Nucleus w/ protons & neutrons Electrons orbit nucleus Bohr found electrons move around nucleus Electron found in energy level Each energy level has different amount of energy

Atoms & Electrons Each energy level can only hold specific number of electrons Level 1: 2 e- Level 2: 8 e- Level 3: 18 e- Level 4-7: 32 e- Valence electron: found in highest energy level (shell) electrons loosely held by nucleus Determine how atom reacts/bonds w/ another atom Determine chemical properties & reactivity of element

Atoms and Electrons Core electrons: electrons found in inner shells/energy levels Valence electrons - occupy outermost shell/energy level Electrostatic force: bonding force that holds 2 or more atoms together b/c electrons are rearranged between the atoms Main group elements: group number = number of valence electrons Elements in same group have same number of valence e- Elements in same group have similar properties b/c same valence e-

Atoms and Electrons Bohr model: shows number of energy levels and number of valence electrons Doesn’t work for transition elements (we will learn why later) Ex: Na (sodium) Group 1 so 1 valence e- K (potassium) (draw model out) Sodium

Atoms and Electrons Energy levels want to be full If can’t be full - better to have 8 e- in shell to be stable 8 e- in last shell = stable electron configuration; less likely to react Noble gases (group 18) 8 valence e- and inert (do not react) Ex. B (boron) Ex. Calcium (Ca)

Stable Electron Configuration Full energy level = stable 8 e- in outer shell = stable Atom can do 2 things to become stable 1) give away electrons in outer shell 2) take electrons from other atoms who need to give the electrons up to be stable Gaining/Losing electrons to become stable allows atoms to chemically react/bond w/ other atoms Atoms must be stable to be happy!

Periodic table and electrons Halogens: group #17, 7 valence e-, like to gain 1 electron to be happy Alkali metals: group #1, 1 valence electron, usually lose it to be stable

Bonding Bonding has to do w/ valence e- Metal: reactivity depends on gaining/losing electrons Depends on how tightly atom holds its valence e- Easier to gain or lose? Less than 4 valence - easier to lose, takes less energy 5 or more valence - atom holds onto e- and gets more from another atom to fill its shell and be stable