Chapter 7.1 Notes Atoms are the smallest form of elements.

Matter is made of what? Yes, matter is made up of atoms. Everything is made up of atoms. Atoms are the smallest particle of an element that has the chemical properties of that element.

How many elements were described at first? In 1789 Antoine Lavoisier created the firs tlist of elements. Lavoisier described 33 elements. He decided that a substance made 2 or more elements would be named after the elements it was made of. –EX: Carbon + 2 Oxygen = Carbon Dioxide.

Why are the elements given a 1 or 2 letter symbol? Many elements are named after people, places or things. Because there are over 100 elements, we have to use symbols with 1 or 2 letters to represent each element. Some elements have the first letter in the name as the symbol. The symbol is always capitalized. Carbon = C, Hydrogen = H, Oxygen = O

Other elements use the first letter and an additional letter in the name as the symbol. In two letter symbols, the first letter is always capitalized and the second letter is always lowercase. –EX: Aluminum = Al, Platinum = Pt Some symbols do not match the name we call them. –EX: Gold = Au, Lead = Pb, Iron = Fe This is because the symbol is based on the Latin name of the element.

Element names and symbols summarized. Element Names: Named after famous people, places and things. –Einsteinium (Es) named after Albert Einstein –Neptunium (Np) named after the planet Neptune Symbols: 1 st letter always capitalized, 2 nd letter always lowercase. –Hydrogen (H), Sulfur (S), Nitrogen (N) –Cobalt (Co), Zinc (Zn), Chlorine (Cl), Silver (Ag)

What is the structure of an atom? Every element is made up of atoms. Every atom of an element is exactly the same. –All oxygen atoms look identical. Every element has as different atom. –Oxygen atoms are different from Carbon atoms. So how do they look?

Atoms are made up of particles called Protons, Neutrons and Electrons. Protons are positively charged particles. (+) Neutrons are particles with no charge. (0) Protons and Neutrons are located in the center of the atom. They are bunched together in the nucleus of the atom.

Electrons are located on the outside of the nucleus and move around the protons and neutrons. The electrons in an atom form an “electron cloud” This electron cloud is where the electron are zipping around the nucleus. –We never know exactly where an electron is, but we do know that it is somewhere inside the cloud. –The positive charge of the proton attracts the electron so it doesn’t fly away.

Draw This!!! Nucleus

So, how big is a single atom? A single atom is about meters in diameter. You could fit millions of atoms into a period printed in the textbook! It would take you 500 years to count the number of atoms in a single grain of salt!

How big are protons, neutrons and electrons? Protons and Neutrons are 2000 times the size of an electron. When calculating the mass of an atom, you only count protons and neutrons. –Electrons have so little mass you ignore them when calculating the mass of an atom! ParticleChargeMass Proton+11 Neutron01 Electron0.0005

What part of an atom determines what element it is? The Atomic Number tells us what element the atom is. Atomic Number protonsThe Atomic Number is the number of protons in the nucleus. –EX: Hydrogen is atomic number 1. That means there is exactly 1 proton in the nucleus of hydrogen. Gold is atomic number 79. Gold has 79 protons in the nucleus. The number of protons in an element never changes!!!

What do you count to get the atomic mass? To get the atomic mass, you count the particles in the nucleus. (Count the protons and neutrons.) Remember, the number of protons in an element never changes… but the number of neutrons can change. neutronsIsotopes are atoms of an element with a different number of neutrons in the nucleus.

Isotopes: The # of protons never changes! The number of neutrons is the only difference. Protons stay the same The # of neutrons changes.

How many neutrons does Chlorine-37 have? The number after the element is the atomic mass of the isotope. Chlorine-37 means 37 total protons+neutrons. Chlorine is atomic number 17. Atomic number 17 = 17 protons in chlorine = # of neutrons = 20 neutrons.

How do atoms form ions? First off, what is an ion? An ion is an atom with missing or added electrons. The number of electrons an element begins with is equal to the number of protons… which is also the same as the atomic number.

Positive Ions When an atom loses an electron, it loses a negative charge. –There are now more positive charges (protons) than negative charges (electrons). A positive ion is smaller in size than the original atom. The electron cloud shrinks. –The protons can pull more on the remaining electrons. Positive ions are written with a “+” after the symbol for each electron lost. –Na +, Ca 2+, Al 3+ –The more positive the ion, the smaller the electron cloud becomes.

Negative Ions Negative Ions form when an atom gains electrons. Because there are more negative charges (electrons) than positive charges (protons) the electron shell expands/gets bigger. –The more negative charges, the bigger it gets! Negative ions are written with a “-” after the symbol for each electron gained. –Cl -, O 2-, N 3-

Chapter 7.2 Notes Elements make up the…

Elements can be organized by similarities. One way scientists organized elements in the past was by their atomic mass. To do this, they had to get the mass of a large chunk of the element and calculate the mass of a single atom. Because there are isotopes of atoms.. (atoms with a different number of neutrons in the nucleus) the atomic mass that was calculated ended up being the average atomic mass of all the isotopes.

Mendeleev and his periodic table. The time is the 1860’s. Mendeleev is working on figuring out patterns in the physical and chemical properties of the known elements of the time. Mendeleev used rows of elements to show similar chemical properties. If the elements were in the same row, they had similar chemical properties. Next, Mendeleev used columns to show atomic mass from lightest to heaviest.

Here is what Mendeleev’s periodic table would have looked like if written like modern periodic tables.

Mendeleev predicted that the holes in his table were elements that were not discovered yet. Many scientists laughed at this idea of undiscovered elements. But, only 6 years after his periodic table, scientists began discovering those predicted elements and the elements had the chemical and physical properties Mendeleev predicted.

So, why is the periodic table organized the way it is? The periodic table of elements is organized by the properties of the elements and their atomic number.

How to read the periodic table. Each “cell” on the table tells us lots of information. –Atomic Number –Chemical Symbol of the element –Name of the element –Average atomic mass of the element.

How does the periodic table in your text book look? Basically the same, but with different colors. In your text book, the color of the chemical symbol means something too! = gas Blue = liquid Black = solid 1 Hydrogen

Groups and Periods Groups are the columns on the periodic table. (Up/down) Groups are also called “family of elements” Elements in the same group have similar chemical properties. They like to react in the same way with the same elements. Their physical properties can be different!

Periods are the rows (left/right) Periods show electron energy cloud “shells” There are 7 energy shells. –Shell 1 holds 2 electrons –Shell 2 holds 8 –Shell 3 holds 8 –Shell 4 holds 18 –Shell 5 holds 18 –Shell 6 and 7 hold a lot more. Basically, periods of elements have similar electron clouds. Empty shells Full Shells