CHAPTER 2 ATOMS AND ELEMENTS LESSON 1 WHAT ARE ATOMS AND ELEMENTS?

DEMOCRITUS, A GREEK PHILOSOPHER, FIRST STATED THAT MATTER WAS MADE OF TINY PARTICLES THAT CAN’T BE DIVIDED. HE PROPOSED THAT THESE PARTICLES WERE TOO SMALL TO BE SEEN.

THEN ARISTOTLE WHO LIVED AFTER DEMOCRITUS SAID MATTER WAS NOT MADE OF PARTICLES. THIS THEORY WAS WIDELY ACCEPTED FOR 2000 YEARS. BUT BOTH WERE NOT BASED ON ANY EVIDENCE.

BY 1800’S, CHEMISTS BEGAN TO MEASURE CHEMICAL REACTIONS. THIS MADE IT POSSIBLE TO JOHN DALTON TO PROPOSE AN ATOMIC THEORY OF MATTER. HIS THEORY WAS THAT ALL MATTER IS MADE UP OF TINY PARTICLES CALLED ATOMS.

STRUCTURE OF AN ATOM. = MORE THAN FIVE MILLION COULD BE LINED UP ACROSS THIS PERIOD. IT WAS THOUGHT THAT ATOMS WERE THE SMALLEST PARTICLES OF MATTER.

SCIENTISTS NOW KNOW ATOMS ARE MADE UP OF SMALLER PARTICLES CALLED SUBATOMIC PARTICLES. THE NUCLEUS IS THE VERY CENTER. IT IS MADE UP OF NEUTRONS AND PROTONS. PROTONS HAVE A POSITIVE CHARGE. A NEUTRON HAS NO CHARGE. THE REST OF THE ATOM IS MADE OF ELECTRONS. THESE HAVE A NEGATIVE CHARGE.

IN 1913, NIELS BOHR PROPOSED A MODEL. HE SAID ELECTRONS CIRCLE THE NUCLEUS AT FIXED DISTANCES FROM IT. THEY ARE CALLED ORBITS. THEY ARE ALSO REFERRED TO AS ENERGY LEVELS. LOW ENERGY ORBITS CLOSER TO THE NUCLEUS. HIGH ENERGY IS AWAY FROM THE NUCLEUS.

A NUCLEUS IS TINY, BUT ALL OF ITS MASS IS THERE. The mass of a proton is nearly 2000 times the mass of an electron. Protons and neutrons have the about the same mass. Electrons and protons have charges that are equally strong.

PART OF WHAT KEEPS AN ATOM TOGETHER IS THE ATTRACTION BETWEEN THE POSITIVE PROTONS AND THE NEGATIVE ELECTRONS. If an atom has more protons, it has a positive charge. If an atom has more electrons than protons it is negatively charged. An atom with the same amount is a neutral atom.

AN ELEMENT IS A SUBSTANCE MADE UP OF ONLY ONE KIND OF ATOM. Gold is element. If a single atom is taken from this nugget, it is still gold. An atom is the smallest unit of an element that has all the properties of that element. Each element has an atomic number.

EACH ELEMENT HAS AN ATOMIC NUMBER. THERE ARE MORE THAN 100 ELEMENTS. AN ATOM OF EACH ELEMENT HAS A SPECIFIC NUMBER OF PROTONS IN ITS NUCLEUS.

THE NUCLEUS OF A HYDROGEN ATOM HAS ONLY ONE PROTON. SO THE ATOMIC NUMBER IS 1.

PLUTONIUM IS 94- ALL ATOMS THAT HAVE 94 PROTONS ARE PLUTONIUM.

MOST MATTER, INCLUDING THE MATTER THAT MAKES UP LIVING ORGANISMS, CONTAINS ONLY A FEW KINDS OF ELEMENTS. FOR EXAMPLE BURGER, GASOLINE AND PAPER ARE MADE UP OF CARBON, HYDROGEN, AND OXYGEN.

THE ATOMS OF MOST ELEMENTS DO NOT OCCUR ALONE. THEY ARE LINKED TOGETHER. TWO OR MORE LINKED TOGETHER FORM A MOLECULE.

WHEN ATOMS ARE LINKED ONLY TO ATOMS OF THE SAME KIND, THEY ARE IN PURE STATE. OXYGEN GAS IS MADE UP OF ONLY OXYGEN MOLECULES WHICH ARE MADE UP OF ONLY TWO OXYGEN ATOMS.

METALS ¼ OF ALL ELEMENTS ARE CLASSIFIED AS NON-METALS THE REST ARE METALS ALL METALS EXCEPT MERCURY ARE SOLID AT ROOM TEMPERATURE

METALS HAVE MANY FAMILIAR PROPERTIES GOLD IS USED IN JEWELRY BECAUSE OF ITS HIGH LUSTER

MOST METALS ARE SAID TO BE MALLEABLE. THEY CAN BE HAMMERED INTO THIN SHEETS THE FOIL USED TO COVER FOOD, IS A THIN SHEET OF ALUMINUM. MOST METALS ARE DUCTILE. THEY CAN BE FORMED INTO WIRES. COPPER AND ALUMINUM ARE USED IN ELECTRIC WIRING.

METALS CONDUCT ELECTRICITY. ELECTRONS FARTHEST FROM THE NUCLEUS OF A METAL ATOM ARE NOT HELD BY JUST THE ATOM. THIS FREEDOM ALLOWS THEM TO CONDUCT ELECTRICITY.

Electrons in materials such as glass, plastic, and rubber are bound tightly to their atoms, so they conduct hardly any electricity. They are called insulators.

METALS ALSO CONDUCT HEAT- HAVE YOU EVER NOTICED THAT A CAR’S METAL PARTS IN THE SUN ARE MUCH HOTTER? THAT’S WHY HANDLES OF POTS AND PANS ARE OFTEN PLASTIC.

ALLOYS- SOME METALS ARE NOT PURE ELEMENTS THEY ARE A MIXTURE OF METALS OR METALS AND OTHER ELEMENTS. BRONZE IS AN ALLOY OF COPPER AND TIN STEEL IS AN ALLOY OF IRON AND CARBON BRASS IS AN ALLOY OF COPPER AND ZINC

ironaluminumNickel copper silverzinc These are pure elements.

Notes The nucleus is the very tiny center of an atom. Metals can be ductile Metals can conduct electricity and heat A plastic handle is the best for a metal pot, because it does not conduct heat as well as the other two materials.

CHAPTER 2 WHAT ARE COMPOUNDS?

DMITRI MENDELEEV- A RUSSIAN CHEMIST ORGANIZED ELEMENTS BY THEIR ATOMIC MASSES Scientists later found that using an order based on the number of protons in one atom of an element- atomic number- is better than one based on atomic mass.

IN THE PERIODIC TABLE, ELEMENTS ARE ARRANGED IN ORDER OF ATOMIC NUMBERS. THEY ARE ALSO ARRANGED SO THAT ELEMENTS WITH SIMILAR PROPERTIES ARE IN THE SAME COLUMN THE ELEMENTS OF A COLUMN ARE PART OF A GROUP

ELEMENTS IN THE SAME GROUP OFTEN HAVE THE SAME NUMBER OF ELECTRONS IN THE OUTER ENERGY LEVELS OF THEIR ATOMS. THIS ARRANGEMENT GIVES THEM THEIR CHEMICAL PROPERTIES.

ALL THOSE ELEMENTS ON THE LEFT SIDE OF THE PERIODIC TABLE ARE METALS (EXCEPT FOR HYDROGEN). METALLOIDS HAVE PROPERTIES OF BOTH METALS AND NON-METALS

EVERY ELEMENT IN THE TABLE HAS AN ABBREVIATION CALLED A CHEMICAL SYMBOL. Even today new elements are being added to the table

COMPOUNDS- A SUBSTANCE MADE OF THE ATOMS OF TWO OR MORE ELEMENTS. WATER IS ONE OF THE MOST IMPORTANT COMPOUNDS. It contains hydrogen and oxygen atoms. The chemical formula shows which elements and how many atoms of each are in a compound. The chemical formula for water is H2O.

The small 2 next to the H means there are two hydrogen atoms in every water molecule. Each water molecule also has 1 atom of oxygen.

A salt molecule has 1 sodium atom and 1 chlorine atoms.

WHEN ATOMS JOIN TO FORM A COMPOUND THEY UNDERGO A CHEMICAL CHANGE. THE PROPERTIES OF THE COMPOUND ARE DIFFERENT FROM THOSE OF THE ELEMENTS IN IT. LIKE HYDROGEN AND OXYGEN BOTH GASES COMBINE TO FORM WATER, A LIQUID COMPOUND.

THEY CAN ALSO REACT. WHEN THEY DO, THEY FORM A NEW PRODUCTS. HYDROCHLORIC ACID CONTAINS HYDROGEN AND CHLORINE ATOMS. IT REACTS WITH SODIUM HYDROXIDE (A BASE) WHICH CONTAINS SODIUM, OXYGEN, AND HYDROGEN ATOMS.

WATER AND SALTS ARE OFTEN THE PRODUCTS OF REACTIONS BETWEEN BASES AND ACIDS.

NOTES COMPOUNDS ARE MADE OF ATOMS OF TWO OR MORE ELEMENTS. THE PERIODIC TABLE IS THE ARRANGEMENT OF ELEMENTS BY SIMILAR PROPERTIES. THEY ARE ALSO ARRANGED BY ATOMIC NUMBER.