C1 - Atomic structure and the periodic table Flashcards

Question

How do calculate the number of subatomic particles?

Answer 1

The symbol for an atom can be written to show its mass number at the top, and its atomic number at the bottom. To calculate the numbers of **subatomic particles** in an atom, use its atomic number and mass number: * number of protons = atomic number * number of electrons = atomic number * number of neutrons = mass number - atomic number

Answer 2

* Isotopes are atoms of the **same** **element** that contain the same number of **protons** and electrons but a different number of **neutrons** * The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number * So, C-14 is the isotope of carbon which contains 6 protons and 6 electrons, but the 14 signifies that it has 8 neutrons (14 - 6 = 8) * It can also be written as ¹⁴C * Isotopes display the **same chemical characteristics** * This is because **they have the same number of electrons in their outer shells, and this is what determines their chemistry** * The difference between isotopes is the neutrons which are neutral particles within the nucleus and add mass only

Answer 3

**The relative atomic mass is the average of the mass numbers of the different isotopes. It is weight for the abundance of each isotope.**

Answer 4

* The relative atomic mass of each element is calculated from the **mass number** and **relative abundances** of all the isotopes of a particular element * The equation below is used where the top line of the equation can be extended to include the number of different isotopes of a particular element present * So, if there were 2 isotopes present then the top line of the equation would read: **(% of isotope A x mass of isotope A) + (% of isotope B x mass of isotope B)**

Answer 5

**Relative atomic masses** can be found in the periodic table. They have the symbol *A*_r. Take care not to confuse mass numbers and relative atomic masses: * mass numbers are always whole numbers (protons or neutrons cannot be split into parts) * relative atomic masses are often rounded to the nearest whole number, but are actually not whole numbers For example, the relative atomic mass of chlorine is 35.5 rather than a whole number. This is because chlorine contains two different isotopes, chlorine-35 and chlorine-37.

Answer 6

* Electrons orbit the nucleus in shells and each shell has a different amount of energy associated with it * The further away from the nucleus, **the more energy a shell has** * Electrons first occupy the shell closest to the nucleus which can hold a maximum of 2 electrons

Answer 7

eThe arrangement of electrons in shells can also be explained using numbers * This method consists of writing down the number of electrons in each shell and separating each number with a comma * There is a clear **relationship** between the outer shell electrons and how the periodic table is designed * The number of notations in the electronic configuration will show the number of shells of electrons the atom has, showing the **period** in which that element is in * The last notation shows the number of outer electrons the atom has, showing the **group** that element is in * Elements in the **same** **group** have the **same** number of outer **shell** **electrons**

Answer 8

* **Period:** The red numbers at the bottom show the number of notations which is 3, showing that a chlorine atom has 3 shells of electrons * **Group:** The last notation, in this case 7, shows that chlorine has 7 outer electrons, and therefore is in group 7

Answer 9

* There are over 100 chemical elements which have been isolated and identified * Elements are arranged on the periodic table in order of **increasing atomic number** * Each element has one proton **more** than the element preceding it * This is done so that elements end up in columns with other elements which have similar properties * The table is arranged in vertical columns called **groups** and in rows called **periods** * **Period:** These are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1 - 7 * E.g. elements in period 2 have two electron shells, elements in period 3 have three electron shells * **Group:** These are the vertical columns that show how many outer electrons each atom has and are numbered from 1 – 7, with a final group called group 0 (instead of group 8) * E.g. group 4 elements have atoms with 4 electrons in the outermost shell, group 6 elements have atoms with 6 electrons in the outermost shell and so on

Answer 10

* The group number of an element which is given on the periodic table indicates the number of electrons in the outer shell (**valence** electrons) * This rule holds true for all elements except **helium**; although is in group 0, it has only **one** shell, the first and innermost shell, which holds only 2 electrons * We can use the group number to predict how elements will react as the number of valence shell electrons in an element **influences** how the element reacts. * Therefore, elements in the same group react **similarly** * By observing the reaction of one element from a group, you can predict how the other elements in that group will react * By reacting two or more elements from the same group and observing what happens in those reactions you can make predictions about reactivity and establish **trends** in reactivity in that group * For example, lithium, sodium and potassium are in group 1 and can all react with elements in group 7 to form an ionic compound * The group 1 metals become **more reactive** as you move down the group while the group 7 metals show a **decrease** in reactivity moving down the group

Answer 11

He noticed that elements with similar chemical properties often occurred in threes called “Triads” such as lithium, sodium and potassium. John Newlands arranged elements in order of **increasing atomic weight**. **He saw that every 8th element reacts in a similar way** so if element 1 is lithium then sodium is element 8. **However by sticking the atoms in order of atomic weight sometimes elements were grouped together** when **they had completely different properties**. Therefore Newlands law of octaves was not really taken seriously by other scientists.

Answer 12

* He organised the elements into **vertical** **columns** based on their properties and the **properties of their compounds** * He then started to arrange them **horizontally** in order of **increasing atomic mass** and as he worked, he found that a **pattern** began to appear in which chemically similar elements fell naturally into the same columns * There were exceptions though as some elements didn't fit the pattern when arranged by atomic mass * **he didn't force an element to fit the pattern, rather he left** **gaps** for **elements that had not yet been discovered** * He also switched the order of the elements to maintain consistency down the columns * He quickly realised that elements with the **same** **properties** should be placed in the **same** **column** * He realised that gaps in the table must correspond to elements that had not yet been discovered or isolated * He used the properties and trends of other elements in the group with the gap to **predict** the properties of these undiscovered elements * When these elements were later discovered and found to fit the pattern developed by Mendeleev, it served to confirm his theories * The existence and properties of “eka-silicon” for example, which we now know as germanium, was predicted by Mendeleev Predictions using gaps Mendeleev left gaps in his table for elements not known at the time. By looking at the properties of the elements next to a gap, he could also predict the properties of these undiscovered elements. For example, Mendeleev predicted the existence of 'eka-silicon', which would fit into a gap below silicon. Another scientist later discovered the missing element, germanium. Its properties were found to be similar to the predicted ones and confirmed Mendeleev's periodic table.

Answer 13

* Once he was finished, Mendeleev thought he had organised the elements systematically but there were still some elements which didn't quite fit in as neatly as he wanted. * This is because **isotopes** were not known in Mendeleev's time, and he made no provisions for them in his table * This meant that there was always going to be some level of inaccuracy in Mendeleev ́s work even though he did also consider the elements chemical properties as well as their atomic mass when sorting them * As soon as the subatomic particles were discovered, the **atomic number** was calculated for each element * This number is used to arrange the elements in the modern-day periodic table which fits with Mendeleev ́s patterns Resolving pair reversals Mendeleev did not know about **isotopes**, but their existence explains [**pair reversals**](https://www.bbc.co.uk/education/guides/z3td6yc/revision). The positions of iodine and tellurium were reversed in Mendeleev's table because: * iodine has one naturally occurring isotope, iodine-127 * the most **abundant** tellurium isotopes are tellurium-128 and tellurium-130 The high relative abundance of these tellurium isotopes gives tellurium the greater relative atomic mass. The atomic number of tellurium is 52 and the atomic number of iodine is 53, so these elements are in the correct order in the modern periodic table.

Answer 14

**The modern periodic table is ordered in terms of atomic number. Protons were not discovered during Medeleev's life.**

Answer 15

Differences in chemical properties Most elements are **metals**. In their chemical reactions, metal atoms lose **electrons** to form positive **ions**. For example: * when magnesium burns in air, each atom loses two electrons to form a Mg²⁺ ion * when sodium reacts with chlorine, each sodium atom loses one electron to form a Na⁺ ion Elements that do not form positive ions in their chemical reaction are **non-metals**. The chemical properties of the compounds of metal and non-metal elements are also different: * most metal oxides are basic * most non-metal oxides are acidic

Answer 16

**Group 0** contains **non-metal** **elements** placed in the vertical column on the far right of the **periodic table**. The elements in group 0 are called the **noble gases**. They exist as single **atoms**. * They are all non-metal, **monatomic** (exist as single atoms), **colourless**, **non-flammable** gases at room temperature * The group 0 elements all have **full outer shells** of electrons; this electronic configuration is **extremely** **stable**

Answer 17

They are very unreactive. * The group 0 elements all have **full outer shells** of electrons; this electronic configuration is **extremely** **stable** * Elements participate in reactions to complete their outer shells by losing, gaining, or sharing **electrons** * The Group 0 elements do not need to do this, because of their full outer shells which makes them unreactive and **inert**

Answer 18

Boiling points This is because, going down group 0: * the atoms become larger * the **intermolecular forces** between the atoms become stronger * more **energy** is needed to overcome these forces

Answer 19

* **Helium is used for filling balloons** and **weather balloons** as it is **less dense** **than air** and **does not burn** * **Neon, argon, and xenon** are used in **advertising** signs * Argon is used to provide an **inert** **atmosphere** for **welding** * Argon is also used to fill **light** bulbs, as like the other noble gases, it has the unusual property of glowing brightly when a high potential difference is applied to the gas under low pressure

Answer 20

* The group 1 metals are known as the alkali metals * They form **alkaline solutions** when they react with water * The alkali metals share similar characteristic chemical properties because they each have one electron in their outermost shell * They are all **soft metals** which can easily be **cut with a knife**, **low** **densities** and **low** **melting** **points** and are **very reactive** (they only need to lose one electron to become highly stable)

Answer 21

Explaining the trend in reactivity When a group 1 element takes part in a reaction, each of its **atoms** loses its outer electron to form a positively charged **ion**. The more easily the ions form, the more reactive the metal. Going down group 1: * the atoms become larger * the **outer electron** becomes further from the **nucleus** * the **force of attractio**n between the **nucleus and the outer electron** **decreases** * **Less energy** is required to o**vercome the force of attraction** as it gets weaker, so the outer **electron is lost** **more easily** * So, the alkali metals get more reactive as you descend the group

Answer 22

* The reactions of the alkali metals with water get more vigorous as you descend the group, as with the other reactions The alkali metals react with water to produce a metal hydroxide and hydrogen. For example, sodium reacts with water: sodium + water → sodium hydroxide + hydrogen 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) Sodium hydroxide is an **alkali**. It is a **base** that **dissolves** in water to form an **alkaline** **solution**. This solution: * has a **pH** greater than 7 * turns **universal indicator** solution blue or purple * Rubidium, caesium and francium will react even more vigorously with air and water than the first three alkali metals * Of the alkali metals, lithium is the **least** reactive (as it is at the top of group 1) and francium would be the **most** reactive (as it’s at the bottom of group 1)

Answer 23

* The metal oxide produced is a dull coating which covers the surface of the metal The group 1 elements react with oxygen from the air to make metal **oxides** which is why the alkali metals tarnish when exposed to the air At room temperature, oxygen reacts with the surface of the metal. This forms a white oxide, which covers the surface. The metal below the surface does not react. The **alkali metals** burn vigorously when heated and placed in a gas jar of oxygen. The oxide forms as white smoke. For example: sodium + oxygen → sodium oxide 4Na(s) + O₂(g) → 2Na₂O(s) The **reactivity** of the group 1 elements increases down the group, so their reactions with oxygen get more vigorous.

Answer 24

* All the group 1 metals react vigorously when heated with chlorine gas to form salts called **metal chlorides** The group 1 elements react vigorously with chlorine. The products of the reactions are chlorides. At room temperature the chlorides are white solids. They dissolve in water to form colourless solutions. For example: sodium + chlorine → sodium chloride 2Na(s) + Cl₂(g) → 2NaCl(s) The reactions with chlorine get more vigorous going down the group.

Answer 25

* The elements in group 7 are known as the halogens * These are fluorine, chlorine, bromine, iodine and astatine * These elements are non-metals that are **poisonous** * All halogens have similar reactions as they each have seven electrons in their outermost shell * Halogens are **diatomic**, meaning they form molecules made of pairs of atoms sharing electrons (forming a single covalent bond between the two halogen atoms) * When halogen atoms gain an electron during reactions, they form -1 ions called halide ions

Answer 26

Flourine is a Yellow gas which is very reactive and poisonous

Answer 27

Green gas which is very reactive and poisonous

Answer 28

Orange liquid

Answer 29

Grey solid

Answer 30

* The melting and boiling points of the halogens **increase** as you go down the group * This is due to increasing intermolecular forces as the atoms become larger, so more energy is required to overcome these forces At room temperature (20 °C), the physical state of the halogens changes as you go down the group * Fluorine and chlorine are **gases**, bromine is a **liquid** and iodine is crumbly **solid** * The colours of the halogens also change as you descend the group - they become darker

Answer 31

When a group 7 element takes part in a reaction, its **atoms** each gain one **electron**. These atoms form negatively charged **ions**. The ions have a stable arrangement of electrons, with a complete outer shell. Going down group 7: * the atoms become larger * the outer shell becomes further from the **nucleus** * the force of attraction between the nucleus and the outer shell decreases * an outer electron is gained less easily * the halogen becomes less reactive

Answer 32

* Chlorine, bromine and iodine react with metals and non-metals to form compounds **Metal Halides** * The halogens react with some metals to form **ionic compounds** which are **metal** **halide** **salts** * The halide ion carries a -1 charge so the ionic compound formed will have different numbers of halogen atoms, depending on the **valency** of the metal * E.g., sodium is a group 1 metal: * 2 Na + Cl₂ → 2 NaCl * Calcium is a group 2 metal: * Ca + Br₂ → CaBr₂ * The halogens **decrease** in **reactivity** moving down the group, but they still form halide salts with some metals including iron * The rate of reaction is **slower** for halogens which are **further** down the group such as bromine and iodine

Answer 33

The halogens react with non-metals such as hydrogen. When a halogen reacts with hydrogen, the product is a **compound** called a hydrogen halide. For example, chlorine reacts with hydrogen: hydrogen + chlorine → hydrogen chloride H2(g) + Cl₂(g) → 2HCl(g) The hydrogen halides are gases at room temperature. They **dissolve** in water to produce **acidic** **solutions**. Hydrogen chloride dissolves in water to produce hydrochloric acid, HCl(aq). The table describes what happens when halogens react with hydrogen. It shows that the reactivity of the elements decreases down the group.

Answer 34

**Displacement Reactions** * A **halogen displacement reaction** occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide * The reactivity of group 7 elements decreases as you move down the group * You only need to learn the displacement reactions with chlorine, bromine and iodine * Chlorine is the most reactive and iodine is the least reactive **Chlorine with Bromine & Iodine** * If you add chlorine solution to colourless potassium bromide or potassium iodide solution a displacement reaction occurs: * The solution becomes orange as bromine is formed or * The solution becomes brown as iodine is formed * Chlorine is **above** bromine and iodine in group 7 so it is more reactive * Chlorine will **displace** bromine or iodine from an aqueous solution of the metal halide chlorine + potassium bromide **→** potassium chloride + bromine Cl₂ + 2KBr **→** 2KCl + Br₂ chlorine + potassium iodide **→** potassium chloride + iodine Cl₂ + 2KI **→** 2KCl + I₂ **Bromine with Iodine** * Bromine is above iodine in group 7 so it is **more** reactive * Bromine will displace iodine from an aqueous solution of the metal iodide bromine + potassium iodide **→** potassium bromide + iodine Br₂ + 2KI **→** 2KBr + I₂

Answer 35

* You could be asked at Higher Tier to provide ionic equations to show what is happening during displacement reactions of the halogens * These are: Cl₂ + 2Br^-→ 2Cl^- + Br₂ Cl₂ + 2I^- → 2Cl^- + I₂ Br₂ + 2I^- → 2Br^- + I₂

Answer 36

* Most of the known metals are **transition** metals and they have typical properties of metals * They are very **lustrous**, they are **hard**, strong and are good conductors of **heat** and **electricity** * They are highly **dense** metals and have very **high melting** points * Transition elements form **coloured compounds.** The transition elements share some **physical properties** with all metals: * they **conduct electricity in the solid and liquid states** * they are **shiny when freshly cut**

Answer 37

**Catalysis** * The transition elements are used extensively as **catalysts** which are substances that speed up the rate of a reaction without being used up in the process * They do not take part in the reaction * Their catalytic characteristics stem from their ability to interchange between a range of oxidation states * This allows them to form complexes with reagents which can easily **donate** and **accept** electrons from other chemical species within a reaction system * Common transition metal catalysts include: * Iron which is used in the **Haber Process** * Vanadium pentoxide (V₂O₅) which is used in the **Contact Process** to produce sulfuric acid * Nickel which is used in the hydrogenation of alkenes **Medicine** * The transition metals are also used in **medicine** and **surgical** applications such as limb and joint replacement * Titanium in particular is useful as it is the only element that can bond with bones due to its high biocompatibility **Other Industrial Applications** * They are also used to form coloured compounds in **dyes** and **paints** for both household and industrial applications * They are used in creating **stained** glass, **jewellery** and in anti-corrosive materials

Answer 38

**Reactions with oxygen** The group 1 elements react quickly with oxygen in the air at room temperature. Most transition elements react slowly, or not at all, with oxygen at room temperature. Some transition metals react with oxygen on heating, for example: copper + oxygen → copper oxide 2Cu(s) + O₂(g) → 2CuO(s) **Reactions with water** The group 1 elements react vigorously with cold water. Most transition elements react slowly with cold water, or not at all. Iron reacts with water and oxygen at room temperature to form hydrated iron(III) oxide, or rust. For more information on rusting, visit the [**Using materials**](https://www.bbc.co.uk/education/guides/ztrwng8/revision) study guide. **Reactions with halogens** The group 1 elements react vigorously with the halogens. Some transition elements also react with halogens, for example: iron + chlorine → iron(III) chloride Fe(s) + Cl₂(g) → FeCl₃(s)

Answer 39

* The transition elements are located between Groups 2 and 3 in the centre of the periodic table * They have all of the typical properties of metals but there are some key differences between them and the Group 1 metals All of the group 1 metals form ions with a +1 charge while the transition metals can form ions with **variable charges** * For example iron can form an Fe²⁺ ion or an Fe³⁺ ion * The transition metals are much **harder, stronger** and **denser** than the group 1 metals, which are very soft and light * They have much **higher melting points** e.g. titanium melts at 1,688 ºC whereas potassium melts at only 63.5 ºC, not far off the average cup of tea! * The transition metals are much **less reactive** than the group 1 metals * The alkali metals react with water, oxygen and halogens while the transition metals either react very slowly or do not react at all * A classic example of this is the reaction with oxygen * A group 1 metal will **tarnish** in the presence of oxygen as a metal oxide is formed * When cut with a knife, the shiny appearance of the metal disappears in seconds as it is covered by the dull metal oxide * Iron on the other hand can take **several weeks** to react with oxygen to form iron oxide (rust) and requires the presence of water