Atomic Structure and Chemical Bonding

Inside an Atom

• The structure of an atom is a nucleus surrounded by one or more electrons.
• Theories about the shape and structure of atoms have evolved over the last 200 years.
• Atoms consist of a nucleus and one or more electrons.
• The nucleus is the central core of an atom, containing protons and neutrons.
• Protons have a positive electric charge (+), while neutrons have no charge (neutral).
• Electrons are energetic particles that move rapidly around the nucleus and have a negative charge (-).
• The valence electrons located farthest from the nucleus participate in forming chemical bonds.
• A chemical bond develops when valence electrons move between atoms, causing the atoms to connect or bond

Atomic Number and Mass

• Every atom of a particular element contains the same number of protons with carbon containing six protons.
• An element's atomic number is the number of protons in its nucleus, and is unique to each element.
• In an atom, protons and electrons are equal in number, so the atom is neutral.
• The atomic mass unit (amu) measures particles in atoms.
• Mass of proton or neutron has one atomic mass unit
• Electrons have less mass, with almost 2,000 electrons equaling one atomic mass unit.
• Most of an atom's mass exists in its nucleus.
• An atom with 6 protons, 6 neutrons, and 6 electrons has a mass of about 12 atomic mass units.
• Atoms of an element always have same number of protons, but the number of neutrons can vary, affecting the mass.
• Neutrons don't affect chemical reactions.
• Atoms of an element share the same chemical properties, despite different masses.

The Role of Electrons

• Impossible to know an electrons location, as they move so fast.
• Electrons moving around the nucleus creates a sphere/cloud of negative charge.
• Most of an atom's mass comes from protons and neutrons.
• Most of an atom's space includes electrons in motion, which is large compared to the space occupied by the nucleus.

Models of Atoms

• Dalton Model (1808): Atoms of different elements have distinct masses, atoms are tiny, solid and can't be divided.
• Thomson Model (1897): An atom is a sphere of positive charge with scattered electrons.
• Nagaoka Model (1904): Atom features a large positively charged sphere with electrons revolving around it like planets around the sun.
• Rutherford Model (1911): Atom is mostly empty space with electrons orbiting a small, positively charged nucleus. Bohr Model (1913): Electrons move in specific layers or shells around the nucleus. Atoms absorb or release energy when electrons shift shells.
• Chadwick Model (1932): Discovered neutrons (particles with a similar mass to protons, but with no electrical charge). Explained atoms are heavier than the total mass of both protons and electrons.
• Modern Model (1920s-Present): Electrons create a negatively charged cloud around the nucleus, with it being impossible to determine the exact location of an electron at any given time.

Organizing the Elements

• By 1830, 55 elements were discovered that had varied properties.
• Dimitri Mendeleev created a system that applied to all the elements in the 1860's.
• Mendeleev noted facts on individual cards, on all properties, including melting point, density, and color.
• He included 2 important findings, atomic mass, and the number of chemical bonds an element had.
• Mendeleev arranged his cards with elements by increasing atomic mass.
• Mendeleev discovered a repetition of properties, and placed the cards with elements into groups of different properties.
• Mendeleev moved element cards and left spaces to predict new elements.
• In Mendeleev's periodic table made in 1869, chemists discovered scandium, gallium, and germanium with predicted properties.
• The word "periodic" means "a regular, repeated pattern."
• In the periodic table, properties of elements repeat in each period (or row_ of the table.

Exploring the Periodic Table

• The modern periodic table has over 100 elements.
• An element's properties can be predicted by looking at it's position in the table.
• One or two-letter symbols identify most elements in the periodic table while providing names. Each column of the periodic table is a group/family with similar properties.
• A row of a periodic table is a period with table becoming wider a periods 2, 4, and 6.
• The atomic number is the number of protons in an atom's nucleus.
• The modern periodic table has arranged elements according to there atomic numbers.
• The atomic mass is the average mass of an element's atoms, increasing with the number.
• The periodic table includes a zigzag to separate metals from non metals.
• The elements are grouped into metals, nonmetals, and metalloids.
• Most chemical symbols derive from Greek or Latin element names.
• Arranged by atomic number, an element's properties can be predicted with atomic number.
• The main body of the periodic table is laid out in 18 verticle coloumns and seven rows (groups/families) with similar elements.
• An element's properties can be predicted by looking at its position in the table.

Periods v Groups

• Each horizontal table row is called a period, which contains a series of different types of elements from different families.
• As you move across the table from left-to-right, properties change and follow a pattern.
• The elements change from very reactive metals to relatively unreactive metal, such as potassium (K), calcium (Ca), nickel (Ni) and copper (Cu),
• The elements change from metalloids and nonmetals, such as arsenic (As) and bromine(Br).
• The last element in a period is always a particularly inactive gas.
• There are seven periods of elements, Periods 2 + 3 have 8 elements, Periods 4 + 5 have 18 elements
• Elements or Period's 6 + 7 have been separated out from the table, appearing as row below its main section
• The periodic table's structure uses the amount electrons, valence electrons, and the structure of atom. Increasing an element's atomic number increases its valence electron, resulting in properties that change in a regular way.
• Elements in the same family will have the same number of valence electrons (a group) for similar properties.

Metals

• Metals are classified based on these physical properties: hardness, shininess, malleability, and ductility.
• Metals are good conductors of heat and electricity.
• Iron (Fe), cobalt (Co), and nickel (Ni) are magnetic
• Very high melting points means the metals are in solid form at room temperature, with liquid mercury (Hg) being the exception.
• A combination with other elements and compounds means most of the metals are reactive.
• Storing under oil in sealed containers, prevents sodium (Na) and potassium (K) reacting explosively if exposed to air/water.
• Gold (Au) + chromium (Cr) are unreactive, which makes gold hold value and chromium is plated on outdoor objects.
• Other metals react slowly with oxygen in the air to perform metal oxides.
• Rust created by the reaction turning a metal surface is called corrosion

Metals cont.

• An alloy, a mixture of metals (steel, brass, and bronze), combines the best properties into a single substance.
• Group 1 metals (alkali metals from lithium to francium) have similar properties and change gradually as you move across the table.
• Never found uncombined in nature, Group 1 contains the most reactive of all metals.
• As elements and metals are very soft/shiny, they could be cut by plastic knife.
• Valence electrons in Group 1 are easily transferred, causing it to be more reactive.
• Sodium + potassium form are the 2 most important alkali metals.
• There are numerous sodium compounds that are found in sea water/salt beds that you need to be alive.
• Batteries and medicines have lithium compounds.
• Alkaline earth metals (Group 2) are fairly hard, gray-white with good electrical conductivity, while are not as reactive.
• As most important metals, magnisum + calium help give off a bright when burning.
• A strong, lightweight aluminum alloy is magnesium.
• Teeth and bones are made up calcium, and helps your muscles work.
• Group 2 like alkali metals contain atoms with 2 valence electrons.
• Transistion metals include familar metals (iron, copper etc.), hard/shiny with colours, conductors, and stable in air/water.
• Lead protects tin a thin layer protecting steel from corrosion.

Metal Contamination

• About 450,000 factories, mines, and dumps are contaminated with toxic metals and have been closed in the US.
• Mercury, cadmium, and lead are toxic metals used in thermometers, medicines, batteries, and paints.
• One cleanup method is to take the contaminated layer of soil to a landfill constructed for hazardous wastes.
• Another method is to cover land with a thick layer of clean soil or substance that stops water from going through, and stop the contamination from moving.
• People want to clean toxic metals, however the worst sites are toxic metals. Or at least, sites need to be fenced off. They do not want the sites used again.
• Construction provides jobs when building new factories, offices, and houses on it.
• Construction sites will provide homes and more jobs, however are in contact with toxic metals which can harm people.

Nonmetals and Metalloids

• Nonmetals have few metal properties and located to the right of the zigzag line in the periodic table.
• Many nonmetals make up very common key components that determine the overall health of a plant of animal life.
• Many nonmetal elements are gases with physical properties at room temperature and a low boiling points.
• With general physical properties, most nonmetals are dull, being solids and brittle (not malleable/ductile) with lower densities and poor conductors of heat/electricity.
• Valence electrons contribute to most nonmetals readily form compounds.
• Group 18 elements don't gain, lose, or share electrons.
• The rest of the nonmetals can gain/share electrons, leading to different element compounds being formed.
• When metals react with nonmetals from Group 17 (easily, a valence electron moves between metal), such as common table salt being created. Group 17 form compounds of nonmetals with metals.
• When combining 2 nonmetals, the atoms share molecules to form molecules (carbon monoxide/dioxide and diatomic molecules (oxygen (O₂), nitrogen (N₂), and hydrogen (H₂).)) and become bonded.
• Group 14 is also the carbon family, contains 4 family member electrons, with carbon being the only nonmetal.
• The chemistry of life happens with carbon; living contains a compounds carbon that contains long chains of carbon atoms.
• The atmosphere/water consists of oxygen.
• Group 15 is the nitrogen family, contains 5 electrons, with nitrogen/phosphorus nonmetals.
• Most of the nitrogen we breath is already in non gas form
• Bacteria combines nitrogen in the area w components (called nitrogen fixation) and plants up take nitrogen.
• The oxygen family (Group 16) has atoms with 6 elections, with oxygen, sulfur, and selenium nonmetals.
• The halogen family (Group 17) contains 7 elements and includes fluorine, chlorine, bromine, iodine, and astatine with atoms that shares similar properties.
• Atoms also can gain/share an electron, with the family members being dangerously active where most compounds are very helpful (like chlorine), while helps toothpaste.
• The noble gas is the Group (18), that do not share high rank mixed with "ordinary people".
• A simple element in hydrogen, contains 1proton/electron and the chemical properties are very different.
• The area between metalloids and nonmetals are 7 elements called semiconductors with both charastics. Conductant depndant on temapture.